Lab Manual

PHYSICS LAB MANUAL

VELTECH HIGH TECH Dr.RANGARAJAN Dr.SAKUNTHALA ENGINEERING COLLEGE

DEPARTMENT OF PHYSICS

(Owned by Vel R.S. Trust, 1997)

Approved by AICTE, New Delhi & Govt. of Tamilnadu & Affiliated to Anna University

PHYSICS LAB MANUAL

(COMMON TO ALL B.E/B.Tech)

Prepared byDepartment of Physics

SEMICONDUCTOR LASER

(A) DETERMINATION OF WAVELENGTH OF LASER USING GRATING

(B) PARTICLE SIZE DETERMINATION

(C) DETERMINATION OF NUMERICAL APERTURE, ACCEPTANCE ANGLE OF AN OPTICAL FIBER AND ANGLE OF DIVERGENCEExpt. No:

Date:AIM

To determine

(a) Wavelength of the given laser source, using a laser source

(b) To find the size of the given particle using the laser source

(c) To measure the numerical aperture and acceptance angle of the given optical fiber.

APPARATUS REQUIRED

1. A laser source, 2. Laser grating, 3. Lycopodium powder, 4. Screen, 5. Scale, 5. Optical fiber 6. Numerical aperture measurement jigFORMULA (a)Wavelength of the given laser source = (b)The size of the particle (d) = metre

(i) To find the wavelength of the laser source : Distance between grating and screen (D) = cm=. 10-2 m Number of rulings in the grating (N) = .lines / meter

S.NoOrder of diffraction (n)Reading for the diffracted imageMean

(=((1+(2)/2 =

Left Side

Right Side

Distance of different orders (Xn)from the central spottan (1=(Xn/D) (1= tan-1(Xn/D)Distance of different orders (Xn)from the central spottan (2=( Xn /D) (2= tan-1(Xn /D)

Unit10-2 m10-2 m10-10 m

(c) (i) Acceptance angle () = degree

(ii) Numerical aperture NA = sinmax (iii)Angle of divergence () = degree Explanation of symbolsSymbol

ExplanationUnit

N

Number of rulings in the grating

lines/meter

Wavelength of the laser source

n

Order of spectrum

Unit

Xn

Distance of the nth order from zeroth order

metre

D

Distance between the laser grating and the screen

metre

D1

Distance between the particle and the screen

metre

d

Distance between the tip of the optical fiber and the aperture of the numerical aperture (NA) Jig.metre

rRadius of the circular opening in NA Jig.

metre

Angle of diffractiondegree

r1Radius of the beam spot at a distance d1metre

r2Radius of the beam spot at a distance d2metre

THEORY

A device for producing spectra by diffraction and interference is known as diffraction grating. While producing diffraction spectra using the particle, the size of the particle should be comparably equal to the wavelength of the source. The diffracted wave

undergoes constructive and destructive interference effect. The intensities of the spectra depend upon the diffraction angle. By measuring the diffraction angle in terms of orders of spectra. The wavelength of the given laser source and the size of the particle can be determined.

Numerical Aperture (NA) and Acceptance Angle: It is the light collecting efficiency of the fiber and is the measure of the maximum amount of light that can be accepted by the fibre.Using Snells law mathematically we can say NA =

Where n1= Refractive index of core

n2= Refractive index of cladding

i.e.

PROCEDURE

(i) To find wavelength of the laser source

The laser source and the laser grating are mounted on separate stands as shown in the fig 11.1. A fixed distance (D) is kept between the laser grating and the screen. The laser source is switched ON and the beam of laser is allowed to fall on the laser grating. The diffracted beams are collected on the screen. The diffracted beams are in the form of spots as shown in Fig 11.2.

In the figure 11.2, the intensity of the irradiance is found to decrease, from zeroth order to higher orders, i.e. the first order is brighter than the second order and so on. The positions X1, X2, X3,..of the spots belonging to the first order, second order, third order etc., on either side of the central maximum are marked on the screen and is noted.

The experiment is repeated for various values of D and the positions of the spots are noted. Then by using the given formula the wavelength of the laser source can be calculated and the mean is taken.

VIVA VOCE1. What is semiconductor diode laser?Semiconductor diode laser is a specially fabricated pn junction diode. It emits laser light when it is forward biased.

2. What is meant by active material in laser?

A material in which population inversion is achieved is called active material.(ii) To find the Size of the given particle : Wavelength of the given laser source () =.. S. No.

Distance between screen and galss plate

10-2 mOrder

(n)

(No.)Distance between the bright point and nth fringe

(Xn) 10-2 mParticle sized

(metre)

1.2.3.

FirstSecondThird

(ii) To find the size of the given particle

Now the laser grating is removed and the size of the particle to be found is introduced. The laser source is switched ON and the light is made to fall on the particle. The screen is moved back and forth until the clear image of the spectrum is seen and the distance between the screen and the particle (D1) is noted. Due to diffraction of laser light by the particle, different orders of spectrum are obtained as shown in fig 11.3. the positions Y1, Y2, Y3,.. of the spots belonging to the first order, second order, third order etc. on either side of the central maximum are noted in a similar way as noted above. Then by using the given formula the size of the particle can be determined.

PRECAUTION

It is dangerous to view the laser light directly. So direct exposure of laser light to eye should be avoided.

VIVA VOCE1. What is laser? The term LASER stands for Light Amplification by Stimulated Emission of Radiation. It is a device which produces a powerful, monochromatic collimated beam of light in which the waves are coherent.

2. What is stimulated emission?

The process of forced emission of photons caused by incident photons is called stimulated emission

3. What are the characteristics of laser radiation?

Laser radiation has high intensity, high coherence, high monochromatism and high directionality with less divergence.

(iii) Measurement of Numerical Aperture and Acceptance Angle

A known length of fiber is taken. One end of the fiber is connected to the laser source and the other end is connected to the numerical aperture (NA) Jig as shown in fig. 11.4. The source is switched ON. The opening in the NA jig is completely opened so that a circular red patch of laser light is observed on the screen. Now the opening in the NA Jig is slowly closed with the knob provided, so that at a particular point the circular light patch in the screen just cuts. The radius of the circular opening (r) of NA Jig at which the circular patch of light just cuts is measured.

The distance between the NA jig opening and the fiber can be measured directly with the help of the calibration in NA jig. By substituting the values in the given formula the numerical aperture can be calculated.

The same procedure can be adopted for various distances between the fiber and the opening of NA jig. The same procedure can also be adopted for various lengths of fiber cables.

By finding the mean of numerical aperture (NA) and substituting it in the given formula the acceptance angle can be determined.

(iii) Measurement of numerical aperture :

S. No.

Length of the given fibre

(metre)Distance between NA Jig opening and the fibre (d)

()Radius of the circular opening in Numerical aperture Jig (r)

()Acceptance angle max=r/d

degree NA = sinmax

no unit

1.

2.

3.

4.

5.

VIVA-VOCE

1. Define numerical aperture

Numerical aperture is defined as the light gathering capability of an optical fibre. It is the sign of the acceptance angle

NA =sin a

2. What is the principle used in fibre optic communication system?

The principle behind the transmission of light waves in an optical fibre is total internal reflection.

3. Define acceptance angle

The maximum angle a with which a ray of light can enter through one end of the fibre and still be total internally reflected is called acceptance angle of the fibre

Determination of angle of divergenceS.Nor 1

(X10-2m ) r 2

(X10-2m ) d 1

(X10-2m ) d 2

(X10-2m ) (deg)

1.

2.

3.

4.

5.

CALCULATION (a) Wavelength of the given laser source =

=..degreeN =..lines/m = .

(b) The size of the particle (d) = metre =..m N=..mD =.m

d =.m

( c) (i) Acceptance angle () = degree

r = . X10-2md = X10-2m

Acceptance angle max=..degree(ii) Numerical aperture NA = sinmaxNA =..(No unit)(iii) Angle of divergence () = degreer1 = X10-2m

r2 = X10-2md1 = X10-2md2 = X10-2m = degree

RESULT(a) The wavelength of the given laser source = .

(b) The size of the given particle

= ..metre

(c) (i) The Numerical aperture of the

given optical fiber

= (No unit) (ii) The Acceptance angle of the

Given optical fiber

=.degree (iii) The Angle of divergence =.....degree

AIR-WEDGE

Expt. No:

Date:

AIM

To find the thickness of a thin wire by forming interference fringes using air-wedge arrangement.

APPARATUS REQUIRED

1. Traveling microscope

2. Sodium vapour lamp

3. Two optically plane rectangular glass plates

4. Condensing lens

5. Reading lens

6. Thin wire

FORMULA

(t) =

Thickness of the thin wire metreExplanation of symbolsSymbolExplanation

Unit

Wave length of sodium lightmetre

lDistance of the wire from the edge of contactmetre

Mean width of one fringemetre

PROCEDURE

An air wedge is formed by keeping two optically plane glass plates in contact along one of their edges. At the other end, thin wire is introduced with its length perpendicular to the length of the plate. The glass plates are tied together in this position by means of rubber band. It is then placed on the horizontal bed plate of the traveling microscope.

The interference pattern can be obtained with the help of the glass plate inclined at 45 to the horizontal plane and a condensing lens (Fig.2.1). Light from the sodium vapour lamp is made to fall vertically on the air wedge. These interference fringes are viewed through the traveling microscope.

(i)To find the fringe width

LC=0.001cm

Order of the bandMicroscope readingWidth of five bands

(x10-2 m)Mean width of one band()

(x10-2 m)

MSR

(x10-2 m)VSC

(div)TR=MSR+

(VSC x LC)

(x10-2 m)

n

n +5

n +10

n +15

n +20

n +25

n +30

n +35

n +40

n +45

n +50

= ........................ x10-2 m

A system of equi-spaced straight alternately dark and bright bands are obtained (Fig.2.2)

The vertical cross wire of the telescope is adjusted to coincide with the centre of well defined dark band near the edge of contact of the glass plates. It is taken as the nth band. The reading on the horizontal scale of the microscope is noted. The microscope is then moved in the same direction by working the horizontal transverse screw and made to coincide with every successive 5th fringe. The readings are noted. This is continued till about 50 fringes are covered. The readings are tabulated. From these readings, the mean width of one fringe () is found.

The distance l between the edges of contact and the wire is measured with the help of the traveling microscope. (Fig2.3). Assuming the wave length of sodium light, the thickness of the thin wire is calculated by using the given formula.

.

(ii) To find the distance between edge of contact and specimen wire

LC=0.001cm

PositionMicroscope readingl = R1 ( R2

(x10-2 m)

MSR

(x10-2 m)VSC

(div)TR=MSR+

(VSC x LC)

(x10-2 m)

Rubber band

(edge of contact)(R1)

Specimen wire

(R2)

l=............................. x10-2 mPRECAUTION

1. The two glass plates must be cleaned and should be optically planed.

2. The movement of the vernier should be in one direction only so as to avoid back lash error.

Scope of this experiment & Engineering application

1. This experiment can be used to determine the thickness of any thin objects like hair, paper, blade etc.

2. The thickness of the insulation of an enameled or cotton covered copper wire can also be found by this method.

VIVA-VOCE

1. What do you mean by interference of light?

When the two waves superimpose over each other, resultant intensity is modified. The modification in the distribution of intensity in the region of superposition is called interference.

2. Is there any loss of energy in interference phenomenon?

No, there is only redistribution of energy i.e., energy from dark place is shifted to bright places.

3. What are interference fringes?

They are alternatively bright and dark patches of light obtained in the region of superposition of two wave trains of light.

4. What type of source is required in division of amplitude?

In division of amplitude a broad source is required so that the whole firm may be viewed together.

5. What is the shape of fringes in wedge shape film?

The fringes in the wedge-shaped film are straight line fringes.

6. When white light is used to illuminate the slit, what is the colour of fringes?

When white light is used to illuminate the slit, the edge of the wedge is dark, with separate coloured fringes from violet to red.

CALCULATIONThickness of wire (t) = mWavelength of sodium light () = 5893 x 10-10m

l = x 10-2m = x 10-2mt = m

RESULT

Thickness of the given thin wire = . metre

ULTRASONIC INTERFEROMETER

Expt. No:

Date :

AIM

(i) To determine the velocity of ultrasonic waves in the medium of different liquids using ultrasonic interferometer.

(ii) To determine the compressibility of the given liquid.

APPARATUS REQUIRED

1. Ultrasonic interferometer

2. Quartz crystal of natural frequency 2 MHz

3. Micrometer and sensor

4. Liquids (Kerosene, Benzene and CCl4) as source.

FORMULA (i) Velocity of ultrasonic waves in a given liquid

v = metre/second(ii) Wavelength of ultrasonic waves = metre

(iii) Compressibility of the liquid K= metre2/newtonExplanation of symbolsSymbolExplanation

Unit

Frequency of the generator which excites the crystalhertz

dDistance moved by the oscillatormetre

nNumbers of oscillations

-

(Density of the liquidkilogram/metre3

DESCRIPTION

Ultrasonic Interferometer technique gives a very accurate value in the measurement of sound velocity. The ultrasonic interferometer consists of following two parts as shown in Fig. 3.1 (i) High frequency generator and (ii) Measuring Cell.

High frequency generator: It generates alternating field or variable frequencies. The frequency generator is used to excite the quartz plate placed at the bottom of the measuring cell at its resonant frequency. The excited quartz crystal generates ultrasonic waves in the experimental liquid in the measuring cell. (Fig 3.2)

Measuring Cell: Measuring cell shown in fig3.3 has a double walled vessel with a provision to maintain temperature constant. At the top of the cell a fine micrometer screw is fitted. With the help of this screw, the reflector plate placed in the cell can be lowered or raised through a known distance. The reflector and the quartz crystal (mounted at the bottom of the cell) are parallel to each other. When the alternating field from the frequency generator is applied to the crystal, it gets into resonant vibrations.

PROCEDURE

The high frequency generator is switched on and the alternating field from the generator is applied to the quartz crystal. The quartz crystal produces longitudinal ultrasonic waves. The ultrasonic waves pass through the liquid and gets reflected at the surface of the reflector plate.

If the distance between the reflector and crystal is exactly a whole multiple of the sound wavelength, standing waves are formed within the medium. This results in the formation of acoustic resonance and causes a change in the potential difference at the generator which excites the crystal. Due to this, anode current of the generator becomes maximum. The change in the anode current can be measured from the micrometer fitted with the frequency generator.

The distance between the reflector and crystal is varied using the micrometer screw such that the anode current decreases from maximum and then increases up to a maximum. The distance between successive maximum or minimum in the anode current is equal to half the wavelength of the ultrasonic waves in the liquid. (fig.3.4)

By noting the initial and final position of the micrometer for one complete oscillation (maxima - minima), one can determine the distance moved by the parallel reflector as shown in figure.3.3

Thus n number of successive maxima or minima is recorded for a distance d. The total distance moved by the micrometer screw is given by

Reading for n oscillation LC = 0.01mmNumber of MaximaReading for Oscillationsd

(x10-3 m)

=

(x10-3 m)

PSR

(x10-3 m)HSC

(div)Correct Reading =PSR+

(HSC x LC)

(x10-3 m)

n

n+5

n+10

n+15

n+20

n+25

n+30

n+35

n+40

n+45

n+50

Mean

d= [(n+m)-n]

d= where m-number of rotations for corresponding oscillations

From the value of , the velocity of the longitudinal ultrasonic waves is calculated using the relation, v = , where is the frequency of the generator which is used to excite the crystal. After determining the velocity of the ultrasonic waves in liquids, the compressibility of the liquid is calculated using the formula K = 1/ 2 where is the density of the liquid. The experiment is repeated for different liquids.

PRECAUTION

1. Do not switch on the generator without filling the experimental liquid in the cell.

2. Remove experimental liquid out of the cell after use, keep it cleaned and dried.3. While cleaning the cell, it should be noted that the gold plating on the crystal is not spoiled or not scratched.CALCULATION(i) Wavelength of ultrasonic waves = metre d=. x10-3m n=.

=....m

(ii) Velocity of ultrasonic v = metre/second =..x10-3 m =2x106 Hz

v =....m/sec

(iii) Compressibility of the liquid K = metre2/newtonv =....m/sec=.....................Kg/m3

K =....m2/N

RESULT

(i) Velocity of ultrasonic waves in a given liquid v = metre/second(ii) Compressibility of the liquidK = metre2/newton

SPECTROMETER GRATING

Expt. No:

Date:

AIM

To find the wavelengths of the prominent spectral lines in the mercury (Hg) source.

APPARATUS REQUIRED

1. Spectrometer

2. Plane transmission grating

3. Sodium vapour lamp

4. Mercury vapour lamp

5. Reading lens. FORMULA

Wavelength of the prominent lines in the mercury (Hg) source = Explanation of symbolsSymbolExplanation

Unit

Angle of diffraction

degree

nOrder of diffraction (spectrum)

-

NNumber of lines per metre in the grating.

lines/metre

PROCEDURE

1. Adjustment of the grating for normal incidence

The initial adjustments of the spectrometer are made as usual. The plane transmission grating is mounted on the grating table. The telescope is released and placed in front of the collimator. The direct reading is taken after making the vertical cross-wire to coincide with the fixed edge of the image of the slit which is illuminated by a source of light (Sodium vapour lamp or mercury vapour lamp).

(i) To find NWavelength of spectral line =5893 X 10-10 m

Colour of spectral linesDiffracted ray readingDifference (2)=2 /2Mean

N=

Left sideRight side

Vernier-AVernier-BVernier-AVernier-BVA A1 A2VB

B1 B2VAVB

MSRVSCTR

(A1)MSRVSCTR

(B1)MSRVSCTR

(A2)MSRVSCTR

(B2)

(deg)(div)(deg) (deg)(div)(deg) (deg)(div)(deg) (deg)(div)(deg) (deg) (deg) (deg) (deg) (deg) Lines/m

Yellow

The telescope is then rotated by an angle 90 (either left or right side) and fixed. The grating table is rotated until on seeing through the telescope the reflected image of the slit coincides with the vertical cross-wire. This is possible only when a light emerging

out from the collimator is incident at an angle 45 towards the collimator. Now light coming out from the collimator will be incident normally on the grating (Fig. 4.1).

2. Wavelengths of the spectral lines of the mercury spectrum

The slit is now illuminated by white light from mercury vapour lamp. The central direct image will be an undispersed image. The telescope is moved on both sides of the direct image, the diffraction pattern of the spectrum of the first order is seen. The readings are taken by coinciding the prominent lines namely violet, green, yellow and red with the vertical cross wire. The readings are tabulated and from this, the angles of diffraction for different colours are determined (Fig.4.2). The wavelengths for different line are calculated by using the given formula. The number of lines per metre in the grating is also calculated.

(ii) Determination of wavelength () of the prominent line of the mercury spectrum

LC = 1'

Order of the spectrum (n) =

N = ..lines/metre

Total Reading = MSR + (VSC LC)

Colour of spectral linesDiffracted ray readingDifference (2)=2 /2Mean

=

Left sideRight side

Vernier-AVernier-BVernier-AVernier-BVA A1 A2VB

B1 B2VAVB

MSRVSCTR

(A1)MSRVSCTR

(B1)MSRVSCTR

(A2)MSRVSCTR

(B2)

(deg)(div)(deg) (deg)(div)(deg) (deg)(div)(deg) (deg)(div)(deg) (deg) (deg) (deg) (deg) (deg) ()

VioletI

VioletII

Blue

Bluish- Green

Green

Yellow

Red

PRECAUTION

1. The grating should be held from the edges and the ruled surface should not be touched.

2. The ruled surface should face away from the collimator.

VIVA VOCE

1. In the present experiment, what class of diffraction does occur and how?

Fraunhofer class of diffraction occurs. Since the spectrometer is focused for parallel rays, the source and the image are effectively at infinite distances from grating.

2. What is plane transmission diffraction grating?

A plane transmission diffraction grating is an optically plane parallel glass plate on which equidistant, extremely close grooves are made by ruling with a diamond point.

3. How are commercial gratings made?

A commercial grating is made by pouring properly diluted cellulose acetate on the actual grating and drying it to a thin strong film. The film is detached from the original grating and is mounted between two glass plates. A commercial grating is called a replica grating.

4. What type of grating do you use for your experiment?

Plane transmission type replica grating.

CALCULATIONNumber of lines per metre in the gratingN= lines/m

n =1 = 5893 x 10-10m

N =.lines/m

Violet-I = =

Violet-II = =

Blue = =

Bluish green = =

Green = =

Yellow = =

Red = =

RESULT(i) Number of lines drawn in the grating per metre = . lines/metre.

(ii) Wavelength of various spectral lines of the mercury spectrum are

V = ..

B = ..

BG = ..

G = ..

Y = ..

R = ..

To find the thickness of the bad conductor (d) Zero error = ..............div

LC = 0.01 cm Zero correction = ..............mmSl.No.PSR

(x10-3 m)HSC

(div)TR=PSR+(HSC x LC)

(x10-3 m)Correct Reading=

TRZC

(x10-3 m)

1.

2.

3.

4.

5.

Mean d = ...................... x10-3 m.

THERMAL CONDUCTIVITY OF A BADCONDUCTOR-LEES DISCExpt. No:Date:

AIM

To determine the thermal conductivity of a bad conductor using Lees disc apparatus.

APPARATUS REQUIRED1. Lees disc apparatus

2. Bad Conductors (card board, glass or ebonite)

3. Thermometers

4. Stop-Clock

5. Steam boiler

6. Screw Gauge7. Vernier Calipers.

FORMULAThermal Conductivity of a bad conductor watt metre-1kelvin-1Explanation of the symbols

SymbolExplanation

Unit

MMass of the metallic disc

kg

SSpecific heat capacity of the material of the disc

J kg-1K-1

Rate of cooling at steady temperature 2 C

C/s

1Steady temperature of a steam chamber

C

2Steady temperature of the metallic disc

C

rRadius of the metallic disc

metre

(i) To find the thickness of the metallic disc (h) Zero error = ..............div

LC = 0.01 mm Zero correction = ..............mmSl.No.PSR

(x10-3 m)HSC

(div)TR=PSR+(HSCxLC)


TRZC

(x10-3 m)

1.

2.

3.

4.

5.

Mean h = ...................... x10-3 m.

hThickness of the metallic disc

metre

dThickness of the bad conductor

metre

PROCEDURE

The thickness of the bad conductor (say card board) and thickness of the metallic disc are determined using a screw gauge. The radius of the metallic disc is found using a vernier caliper. The mass of the metallic disc is also found using a common balance. The readings are tabulated.

The whole Lees disc apparatus is suspended from a stand as shown in figure. The given bad conductor is placed in between the metallic disc and the steam chamber. Two thermometers T1 and T2 are inserted in the respective holes.

Steam from the steam boiler is passed in to the steam boiler until the temperature of the steam chamber and the metallic disc are steady. The steady temperature 1 of the steam chamber and the steady temperature 2 of the metallic disc recorded by the thermometers are noted.

Now the bad conductor is removed and the steam chamber is placed in direct contact with the metallic disc. The temperature of the disc rapidly rises. When the temperature of the disc rises about 10C above 2 C (steady temperature of the disc), the steam chamber is carefully removed, after cutting off the steam supply.

When the temperature of the disc reaches 10 C above the steady temperature of the disc i.e., (2+10)C, a stop clock is started. Time for every 1C fall of temperature is noted until the metallic disc attains a temperature (2-10)C.

Determination of the rate of cooling of metallic disc Steady temperature in the metallic disc (2) =..................CTemperature ()

CTime (t)

Second

GRAPH

A graph is drawn taking time along the X axis and temperature along the Y axis. The cooling curve is obtained. To obtain the rate of cooling (d/dt)2 from this graph, a triangle is drawn by taking 1C above and 1C below the steady temperature 2. Then the slope AB / BC gives the rate of cooling at (d/dt) at 2.

From these readings and using the given formula the thermal conductivity of the bad conductor is calculated.

CALCULATIONThermal Conductivity of a bad conductor

watt metre-1kelvin-1M = ..kg

S = ... J kg-1K-1

= . Cd = x10-3m

r = .x10-2m

h = x10-3m1 = C2 = CK = watt metre-1kelvin-1

RESULT

Thermal conductivity of the given bad conductor =Wm-1K-1.

B H CURVE USING CROExpt. No:

Date:

AIM

To determine the hysteresis loss in the transformer core using B H curve unit.

APPARATUS REQUIRED

1. B H curve unit

2. Cathode Ray Oscilloscope (CRO)

3. Patch cords

FORMULA

Hysteresis loss = Area of the loop

joule cycle-1metre-3Explanation of the symbols

SymbolExplanationUnit

Number of turns in the primary coil -

Number of turns in the secondary coil-

VVolume of the coremetre3

Vertical sensitivity of CROVm-1

Horizontal sensitivity of CROVm-1

&

Resistances in the circuitohm

CCapacitance of the capacitor in the circuitfarad

PROCEDURE

The experimental arrangement is shown in the figure 6.1

One of the specimens used in the unit is made using transformer stampings. There are two windings on the specimen (primary and secondary). The primary is fed to low A.C voltage (50 Hz). This produces a magnetic field H in the specimen. The voltage across R1 (resistance connected in series with primary) is proportional to the magnetic field

It is given to the input of the CRO. The A.C magnetic field induces a voltage in the secondary coil. The voltage induced is proportional to dB/dt.

This voltage is applied to passive integrating circuit. The output of the integrator is proportional to B and fed to the vertical input of the CRO.

As a result of the application of voltage proportional to H the horizontal axis and a voltage proportional to B is the vertical axis, the loop is formed as shown in fig 6.3. A measurement of the area of the loop leads to the evaluation of energy loss in the specimen.

The top view of the unit is shown in the figure 6.2. There are 12 terminals on the panel, sin patch cords are supplied with the kit.

The value of R1 can be selected by connecting terminal D to A, B or C (A-D=50 ohm; B-D=150 ohm; C-D=50 ohm)

A is connected to D. The primary terminals of the specimen is connected to p,p secondary to s,s terminals. The CRO is calibrated as per the instructions given the Instruction Manual of CRO. CRO is adjusted to work on external mode (the time base is switched off). The horizontal and vertical position controls are adjusted such that the spot is at the centre of the CRO screen.

The terminal marked GND is connected to the ground of the CRO. The H is connected to the Horizontal input of the CRO. The terminal V is connected to the vertical input of the CRO. The power supply of the unit is switched on. The Hysteresis loop is formed. The horizontal and vertical gains are adjusted such that the loop occupies maximum area on the screen of the CRO. Once this adjustment is made, the gain controls should not be disturbed. The loop is traced on a translucent graph paper. The area of the loop is estimated,

The connections from CRO is removed without disturbing the horizontal and vertical gain controls. The vertical sensitivity of the CRO is determined by applying a known A.C voltage say 1 volt (peak to peak).

If the spot deflects by x cms for 1 volt, the vertical sensitivity is 1/(x x 10-2) (volt/m). let it be SV. The horizontal sensitivity of CRO is determined by applying a known A.C voltage say 1 volt (peak to peak). Let the horizontal sensitivity be SH (volt/m).

The hysteresis loss is calculated by using the given formula.

OBSERVATIONS

Number of turns in the primary N1 = ...

Number of turns in the secondary N2 = Resistance

R1 = ..ohmResistance

R2 = ..ohmCapacitance of the capacitor C = F

Vertical sensitivity of CRO

SV =...Vm-1Horizontal sensitivity of CRO SV =...Vm-1CALCULATION

Area of the loop =..m2

(from the graph)

Hysteresis loss = Area of the loop joule cycle-1metre-3RESULTEnergy loss = . joules cycle -1 metre-3

TORSIONAL PENDULUMExpt. No:

Date:

AIM

To determine (i) the moment of inertia of the disc and (ii) the rigidity modulus of the material of a wire by torsional oscillations.

APPARATUS REQUIRED

1. Torsional pendulum (uniform circular disc suspended by a wire)

2. Two equal cylindrical masses

3. Stop-clock

4. Screw gauge

5. Metre scale.

FORMULA

Moment of inertia of the disc I = kg m2

Rigidity modulus of the material of the wire n = newton/metre2Explanation of the symbolsSymbolExplanation

Unit

mMass (mass of one of the cylinders) placed on the disckg

d1Closest distance (minimum) between suspension wire and the centre of mass of the cylindermetre

d2Farthest distance (maximum) between suspension wire and the centre of mass of the cylindermetre

T0Time period without any mass placed on the discsecond

T1Time period when equal masses are placed at a distance d1second

T2Time period when equal masses are placed at a distance d2second

LLength of the suspension wiremetre

RRadius of the wire metre

(i) To find the time periods of the disc at different stages

Length of the suspension wire (l) =............................. x10-2 m

Position of the equal massesTime for 20 oscillationsTime for 1 oscillation

(sec)

Trail -1

(sec)Trail -2

(sec)Mean

(sec)

Without

Symmetrical

masses

With masses at closest distance

d1 = ......... x10-2 m

With masses at maximum distance

d2 = ......... x10-2 m

PROCEDURE

One end of a long, uniform wire whose rigidity modulus is to be determined is clamped by a vertical chuck. To the lower end, a heavy uniform circular disc is attached by another chuck. The length of the suspension l is fixed to a particular value (say 60 cm or 70 cm). The suspended disc is slightly twisted so that it executes torsional oscillations. Care is taken to see that the disc oscillates without wobbling.

The first few oscillations are omitted. By using the pointer, (a mark made in the disc) the time taken for 20 complete oscillations are noted. Two trials are taken. The mean time period T (time for one oscillation) is found.

Two equal cylindrical masses are placed on the disc symmetrically on either side, close to the suspension wire (at the minimum distance). The closest distance d1 from the centre of the mass of the cylinder and the centre of the suspension wire is found. The disc with masses at distance d1is made to executive torsional oscillations by twisting the disc. The time taken for 20 oscillations is noted. Two trials are taken. The mean time period T1 is determined.

Two equal masses are now moved to the extreme ends so that the edges of masses coincide with the edge of the disc and the centres are equi-distant. The distance d2 from the centre of the mass of the cylinder and the centre of the suspension wire is noted. The disc with masses at distance d2 is allowed to execute torsional oscillations by twisting the disc. The time taken for 20 oscillations is noted and time period T2 is calculated.

The mass of one of the cylinders placed on the disc is found. The diameter of the wire is accurately measured at various places along its length with screw gauge. From this, the radius of the wire is calculated. The moments of inertia of the disc and rigidity modulus of the wire are calculated using the given formulae.(ii) To find the radius of the suspension wire (r) Zero error = ..............div

LC = 0.01 mm Zero correction = ..............mmSl.No.PSR

(x10-3 m)HSC

(div)TR=PSR+(HSCxLC)


TRZC

(x10-3 m)

1.

2.

3.

4.

5.

Mean d = ...................... x10-3 m.

Mean radius r = = ...................... x10-3 m.

PRECAUTION

1. The circular disc must be horizontal.

2. The suspension wire should be well clamped, thin, long and free from kinks.

3. The motion of the circular disc should be purely rotational in horizontal plane, up and down and lateral oscillations must be completely checked.

4. Equal masses should be placed diametrically opposite with respect to the centre of the disc.

VIVA-VOCE1. What is torsional pendulum?

A body suspended from a rigid support by means of a long and thin elastic wire is called torsional pendulum.

2. What is the rigid body you can use for a torsional pendulum?

Sphere, cylinder or circular disc.

3. Why is it called a torsional pendulum?

As it performs torsional oscillations, it is called torsional pendulum.

4. What is the type of oscillation?

This is of simple harmonic oscillation type.

5. On what factors do the time period depends?

It depends upon (i) moment of inertia of the body (ii) rigidity of wire i.e., length, radius and material of the wire.

6. What type of wire do you prefer for this experiment?

Thin and long metallic wire.

7. How will you determine the rigidity of fluids?

As fluids do not have a shape of their own, hence they do not possess rigidity. Hence there is no question of determining it.

Scope of this experiment

By doing this experiment, we understand an important concept of elasticity. The elastic characteristics of different materials like steel, copper wire etc can be analyzed.

CALCULATIONMoment of inertia of the disc I = kgm2Time period of oscillation (without masses) T0 = . second

Time period when masses are at distance d1 T1 =. secondTime period when masses are at distance d2 T2 =. second

Closest distance between suspension wire d1 = x 10-2m

and the centre of mass of the cylinder

Farthest distance between suspension wire d1 = x 10-2m

and the centre of mass of the cylinder

Mass of one of the cylinder m = x 10-3 kgLength of the suspension wire l = x 10-2mMean radius of the wire r = x 10-3m

I = .kg.m2

Rigidity modulus of the material of the wire n = N/m2

n = .N/m2

RESULT

Moment of inertia of the disc (I) = .. kg m2

Rigidity modulus of the material of given wire (n) = Nm-2

YOUNGS MODULUS NON UNIFORM BENDING

Expt No:

Date:

AIM

To find the Youngs modulus of the material of a uniform bar (metre scale) by non uniform bending.

APPARATUS REQUIRED


2. Two knife edge supports

3. Weight hanger with set of weights

4. Pin

5. Metre scale

6. Vernier Calipers

7. Screw gauge

FORMULA

Youngs modulus of the material of the beam (metre scale) E = N/m2Explanation of the symbolsSymbolExplanation

Unit

yMean depression for a load Mmetre

gAcceleration due to gravity m/s2

lDistance between the two knife edgesmetre

bBreadth of the beam (metre scale)metre

dThickness of the beam (metre scale)metre

mLoad appliedkg

(i) To find depression y

Total Reading (TR) = MSR + (VSC X LC)M = ..x 10-3kg LC = 0.001 cm

Sl.No.

Load

(x 10-3kg)Microscope ReadingsMean

(x 10-2m)Depression y for M kg

(x 10-2m)

LoadingUnloading

MSR

(x 10-2m)VSC

(div)TR

(x 10-2m)MSR

(x 10-2m)VSC

(div)TR

(x 10-2m)

1.W

2.W+50

3.W+100

4.W+150

5.W+200

6.W+250

7.W+300

Mean y

Mean y = x 10-2m

PROCEDURE

The weight of the hanger is taken as the dead load W. The experimental bar is brought to elastic mood by loading and unloading it a number of times with slotted weights. With the dead load W suspended from the mid point, the microscope is adjusted such that the horizontal cross-wire coincides with the image of the tip of the pin. The reading of the vertical scale is taken.

The experiment is repeated by adding weights in steps. Every time the microscope is adjusted and the vertical scale reading is taken. Then the load is decreased in the same steps and the readings are taken. From the readings, the mean depression of the mid point for a given load can be found. The length of the bar between the knife edges is measured l.

The bar is removed and its mean breadth b is determined with a vernier caliper and its mean thickness d with a screw gauge.

From the observations, Youngs modulus of the material of the beam is calculated by using the given formula.

(ii) To find breadth of the beam

LC = 0.01 cm Zero error = div

Zero correction = cm

Sl.No.MSR

(x 10-2m)VSC

(div)TR = MSR+(VSC X LC)

(x 10-2m)Correct reading =TRZC

(x 10-2m)

1.

2.

3.

4.

5.

Mean b = x 10-2m

PRECAUTIONS

1. The beam must be kept horizontal.

2. While taking readings, the microscope must be moved in the same direction so as to avoid the back-lash error.

3. After loading or removing weights, some time must be allowed before taking the readings.

4. To find the thickness of the beam (d)

LC = 0.01mm Zero error = div

Zero correction = mm

S. No.PSR

(x 10-3m)HSC

(div)Observed Reading =

PSR + (HSC LC)

(x 10-3m)Correct Reading =

OR ZC

(x 10-3m)

1.

2.

3.

4.

5.

Mean (d) = 10-3 mVIVA-VOCE

1. What is Youngs modulus?

Youngs modulus is defined as the ratio of the longitudinal stress to the longitudinal strain.

2. What is a beam?

When the length of a rod of uniform cross-section is very large compared to its breadth such that the shearing stress over any section of the rod can be neglected, the rod is called a beam.

3. How are longitudinal strain and stress produced in your experiment?

Due to depression, the upper or the concave side of the beam becomes smaller than the lower or the convex side of the beam. As a result, longitudinal strain is produced. The change in length will be due to the forces acting along the length of the beam. These forces will give rise to longitudinal stress.

4. How do you ensure that in your experiment the elastic limit is not exceeded?

The consistency in the readings of depressions both for increasing load and decreasing load indicates that in the experiment the elastic limit is not exceeded.

5. Which dimension breadth, thickness, or length of the bar-should be measured very carefully and why?

The thickness of the bar should be measured very carefully since its magnitude is small and it occurs in the expression E in the power of three. An inaccuracy in the measurement of the thickness will produce the greatest proportional error in E.

6. What is the SI unit of Youngs modulus?

newton/m27. Will the value of Youngs modulus obtained by you change if the length, thickness or breadth of the bar is altered?

No

8. Why do you place the beam symmetrically on the knife edges?

To keep the reaction at the knife edges equal in conformity with the theory.

CALCULATIONYoungs modulus of the material of the beam (metre scale) E = N/m2Load applied M = .kg

Acceleration due to gravity g = 9.8 m/sec2Distance between two knife edges l = x10-2m

Breadth of the beam b = x10-2mThickness of the beam d = x10-2mDepression for load applied y = x10-2mE = N/m2

RESULT

Youngs modulus of the material

of the given bar (metre scale) = ..newton/metre2

VISCOSITY OF A LIQUIDBY POISEUILLES METHODExpt. No:

Date:

AIM

To find the co-efficient of viscosity of a liquid by Poiseullies method.

APPARATUS REQUIRED1. Graduated burette without stopper, 2. Retort stand with clamp, 3. Capillary tube, 4. Beaker, 5. Water6. Stop watch7. Meter scale

8. Rubber tube9. Pinch cock

FORMULA

Co-efficient of viscosity of the given liquid Nsm-2Explanation of the symbols

Symbol

ExplanationUnit

gAcceleration due to gravity

m/s2

Density of the liquid

kg/m3

rRadius of the capillary tube

metre

lLength of the capillary tube

metre

VVolume of the liquid collected

metre3

h(h1+h2)/2 - h0

metre

h1Height from table to initial level of water in the burette

metre

Measurement of time for liquid flow

h0 = X10-2m

Sl.No.Burette reading

(cc)Time note while crossing level

(second)Range

(cc)Time for flow of 5 cc liquid

(second)Height of initial reading h1

( X10-2m)

Height of final reading h2

( X10-2m)

Pressure head

h = (h1+ h2 )/2- h0

( X10-2m)ht

( X10-2m-second)

1.

00-5

2.

55-10

3.

1010-15

4.

1515-20

5.

2020-25

6.

2525-30

7.

3030-35

8.

3535-40

9.

4040-45

10.

4545-50

11.

50

h2Height from table to final level of water in the burette

metre

h0Height from table to mid portion of the capillary tube

metre

tTime taken for the liquid flow

second

PROCEDURE

A clean dry burette is fixed to a stand. A capillary tube is connected to the burette by means of a rubber tube and is held parallel to the table so that the flow of liquid is streamlined.

A given liquid is filled in the burette and the level of liquid reaches the zero mark, the stop-clock is started and the time is noted, when liquid level crosses 0, 5, 10, 15 ...45cc. The time taken for the flow of 5 cc of liquidt is thus determined. It is seen that as height h decreases the time of flowt increases. The product ht is a constant. The mean value of ht is substituted to calculate co-efficient of viscosity of the liquid.

To find the radius (r) of the capillary tube:

The capillary tube is held horizontally. The horizontal crosswire of telescope of the traveling microscope is made to coincide with the top of the bore of the capillary tube. The reading in the vertical scale is taken. Again, the horizontal crosswire is adjusted to be tangential to the bottom of the bore of the capillary tube. The readings in the vertical scale are taken. The difference between the two readings gives the diameter of the bore.

Similarly, using vertical crosswire, the readings in the horizontal scale corresponding to left and right edges of the bore of the capillary tube are taken. The difference between the two readings gives the diameter. The readings are tabulated. The average diameter and hence the radius are determined.

Using the mean value of ht, the co-efficient of viscosity of the given liquid is calculated.

To find the radius of the capillary tube (r)

LC = 0.001 cm

Horizontal cross wire

Vertical cross wire

PositionMSR

( X10-2m)

VSC

(div)TR

( X10-2m)

PositionMSR

( X10-2m)

VSC

(div)TR

( X10-2m)

Top

Left

Bottom

Right

PRECAUTIONThe motion of the liquid must be stream line and care must be taken to ensure that the flow of liquid doesnt become turbulent. VIVA-VOCE 1. What is viscosity and define the coefficient of viscosity? In the presence of a relative motion between two layers of a liquid, an opposing tangential force sets in between the layers to destroy the relative motion. This property of liquid is termed viscosity and is analogous to friction. The tangential force acting per unit area over two adjacent layers of the liquid for a unit velocity gradient is referred to as the coefficient of viscosity. 2. How does the coefficient of viscosity changes with temperature?

The coefficient of viscosity changes with rise in temperature in case of liquids. But for gases it increase with rise with temperature.

3. Which quantity requires greatest care in its measurement? Why?

The radius of the capillary tube requires greatest care in its measurement. Since it

occurs in the forth power in the expression of . Thus a small measurement of r, which itself small, will contribute to a large proportional error in . The tube selected must therefore be uniform and its radius be measured very carefully.4. Can you use this method for all types of liquids?

No, this method can be suitably applied for liquids of low viscosity. For highly viscous liquids, Stokes method can be used.

5. Is there any difference between friction and viscosity?

Friction and viscosity have some similarities and some differences between them. For liquids at rest, friction works but viscosity doesnt because viscosity arises only when there is a relative motion between the layers of a liquid.

CALCULATIONCo-efficient of viscosity of the given liquid Nsm-2 = .. kg/m3g = .. m/s2r = ..x10-2m

ht =. x10-2m-second

l = x10-2mV =.. metre3 = --------------- newton-second/metre2

RESULT:

The co-efficient of viscosity of a given liquid = .Nsm-2

DISPERSIVE POWER OF A PRISM-SPECTROMETERExpt. No:

Date:

AIM

To find the dispersive power of the material of the prism using spectrometer.

APPARATUS REQUIRED1. Spectrometer 2. Mercury vapour lamp

3. Glass prism

4. Reading lens

FORMULAE

Refractive index of the prism (No unit)

Dispersive power of the material of the prism (No unit)Explanation of the symbols

SymbolExplanationUnit

AAngle of the prismdegree

DAngle of minimum deviation degree

Refractive index of the prism for violet line-

Refractive index of the prism for red line-

Refractive index of the prism for yellow line -

PROCEDURE

The initial adjustment of the spectrometer namely adjustment of eye piece for distinct vision of cross wires, adjustment of telescope for the distant object and collimator for parallel rays are made as usual. The slit of the collimator is illuminated by the mercury vapour lamp.

To find the angle of minimum deviation (D) Spectrometer readings

TR = MSR + (VSC X LC) LC = 1'S.No.Refracted ray readingsVernier AVernier BAngle of minimum deviation (D)Mean D =

(deg)

(No unit)

Lines of the spectrumMSR

( deg)VSC

(div)TR

( deg)MSR

( deg)

VSC

(div)TR

( deg)

Ver A

R1~R2

( deg)

Ver B

R1~R2

( deg)

1.Violet-I

2.Violet-II

3.Blue

4.Bluish green

5.Green

6.Yellow

7.Orange

8.Red

(i) Determination of angle of prism (A)

The given prism is mounted vertically at the centre of the prism table with its refracting edge facing the collimator. Now the parallel rays of light emerging out from the collimator falls almost equally on the two faces of the prism ABC as shown in fig. The telescope is turned to catch the reflected image from one face of the prism and fixed in that position. The tangential screw is adjusted until the vertical cross-wire coincides with the fixed edge of the image of the slit.

The readings on both the verniers are noted. Similarly the readings corresponding to the reflected image of the slit on the other face are also taken. The difference between the two readings of the same vernier gives twice the angle of the prism. Hence, the angle of the prism A is determined.

(ii) Determination of angle of minimum deviation (D)

The prism table is rotated so that the beam of light from the collimator is incident on one face of the prism and emerges out from the other face. The telescope is rotated to catch the refracted image of the yellow slit. The prism table is rotated in such a direction so that the refracted image move towards the direct beam. The telescope is rotated carefully to have the image in the field of view. At one stage, the image stops momentarily and turns back. This is the position of the minimum deviation (fig)

The telescope is rotated and made to coincide with the violet slit. The telescope is fixed in this position and refracted ray reading of the telescope is noted. The experiment is repeated for red slit. The prism is removed and the direct reading of the slit is taken. The difference between the direct reading and the refracted ray reading corresponding to the minimum deviation gives the angle of minimum deviation D. The dispersive power is calculated using the given formula.

PRECAUTION

1. All the initial adjustments of the spectrometer must be done before starting the experiment.

2. During rotation of the telescope, if the vernier zero crosses the zero mark of the main circular scale, then the latter should be considered as 360 and calculations should made accordingly.

3. The polished faces of the prism should not be touched.

To find the angle of prism (A) Spectrometer readings

TR = MSR + (VSC X LC) LC = 1'Reflected rayVernier AVernier B

Lines of the spectrumMSR

( deg)

VSC

(div)TR

( deg)

MSR

( deg)

VSC

(div)TR

( deg)

Readings of image reflected from one face (left)

(R1)(R1)

Readings of image reflected from one face (right)

(R2)(R2)

2A= R1~R2

2A= R1~R2

Mean 2A =

Mean A =

VIVA-VOCE1. What is a spectrometer?

It is an instrument used for analyzing the spectrum of a source of light.

2. What is the function of a collimator in a spectrometer?

The main function of the collimator is to produce a parallel beam of light.

3. What is the condition for obtaining minimum deviation

The deviation is minimum when the angles of incidence and the emergence are equal.

4. Define refractive index

The ratio of the sine of the angle of incidence of the sine of angle of refraction is constant for any two media, i.e., a constant known as refractive index.

5. How does refractive index change with wavelength of light?

Higher the wavelength, smaller is the refractive index.

6. Does the deviation depend on the angle of the prism?

Yes, greater the angle of the prism, more is the deviation.

7. Define dispersive power of a prism.

Dispersive power indicates the ability of the material of the prism disperse the light rays. It is defined as the ratio of the angular dispersion to the derivation of the mean ray.

CALCULATIONRefractive index =

=

Dispersive power of the material of the prism

RESULT 1. Angle of prism = .. degree2. Angle of minimum deviation = .. degree

3. Refractive index of the given prism = . (No unit)4. Dispersive power of the prism = . (No unit)

YOUNGS MODULUS UNIFORM BENDING

Expt. No:

Date:

AIM

To determine the Youngs modulus of the material of the beam (metre scale) by uniform bending.

APPARATUS REQUIRED


2. Two knife edges

3. Two set of weights

4. Pin

5. Metre scale

6. Vernier caliper

7. Screw gaugeFORMULA

Youngs modulus of the material of the beam (metre scale)

EMBED Equation.3 newton/metre2Explanation of the symbolsSymbolExplanation

Unit

yElevation for a load Mkg

MLoad appliedkg

gAcceleration due to gravity m/s2

aDistance between the point of application of load and the nearest knife edgemetre

lDistance between the two knife edgesmetre

bBreadth of the beam (metre scale)metre

dThickness of the beam (metre scale)metre

(i) To find depression y

Total Reading (TR) = MSR + (VSC X LC)M = ..x 10-3kg LC = 0.001 cm

Sl.No.

Load

(x 10-3kg)Microscope ReadingsMean

(x 10-2m)Depression y for M kg

(x 10-2m)

LoadingUnloading

MSR

(x 10-2m)VSC

(div)TR

(x 10-2m)MSR

(x 10-2m)VSC

(div)TR

(x 10-2m)

1.W

2.W+50

3.W+100

4.W+150

5.W+200

6.W+250

7.W+300

Mean y

Mean y = x 10-2mPROCEDURE

The given beam is symmetrically supported on two knife edges and weight hangers are suspended at equal distance from the knife edges. A pin is fixed vertically at the mid point of the beam. A suitable dead load W is suspended from each hanger.

Using traveling microscope, the reading corresponding to the tip of the pin is taken. The load is increased in steps of 50 gram up to 250 gram and the readings of the microscope are noted.

Readings are also taken when the load in each hanger is decreased in the same step. The readings are tabulated and the mean elevation is determined.

The length l and a are measured. The breadth (b) of the scale is determined using vernier caliper. The thickness (d) of the scale is determined using a screw gauge. From the observations, the Youngs modulus of the material of the scale is calculated.

(ii) To find breadth of the beam

LC = 0.01 cm Zero error = div

Zero correction = cmSl.No.MSR

(x 10-2m)VSC

(div)TR = MSR+(VSC X LC)

(x 10-2m)Correct reading =TRZC

(x 10-2m)

1.

2.

3.

4.

5.

Mean b = x 10-2mPRECAUTION

1. The beam must be kept horizontal

2. Since the value of thickness (d) is small and it occurs in the third power, it must be measured carefully with a screw gauge.

3. While taking readings, the microscope must be moved in the same direction, so as to avoid the back lash error.

4. After loading or removing weights, some time must be allowed before taking the readings.

(iii) To find the thickness of the beam (d)

LC = 0.01 mm Zero error = div

Zero correction = mm

S. No.PSR

( 10-3 m)HSC

(div)Observed Reading =

PSR + (HSC LC)

( 10-3 m)Correct Reading =

OR ZC

( 10-3 m)

1.

2.

3.

4.

5.

Mean (d) = 10-3 mVIVA-VOCE

1. What is elasticity?The property of the body to regain its original shape or size, after the removal of deforming force is called elasticity.

2. What are elastic bodies?

Bodies which regain its original shape or size, after the removal of deforming force is called elastic bodies.3. Define Youngs modulus of elasticity?

Within the elastic limit the ratio of longitudinal stress to longitudinal strain is called the Youngs modulus of elasticity. It is denoted by the letter E

Youngs modulus of elasticity (E) =

EMBED Equation.3 Unit: newton/metre24. What are the factors affecting elasticity?5. Stress

6. Change in temperature

7. Impurities

8. Hammering, rolling and annealing.

9. Crystalline nature

5. What is uniform bending?

The beam is loaded uniformly on its both ends, the bent beam forms an arc of a circle. The elevation in the beam is produced. This bending is called uniform bending. CALCULATIONYoungs modulus of the material of the beam (metre scale) newton/metre2Load applied M = .kgAcceleration due to gravity g = 9.8 m/sec2Distance between the point of load a = x10-2mApplication of load and the nearest

Knife edgeDistance between two knife edges l = x10-2mBreadth of the beam b = x10-2mThickness of the beam d = x10-3mDepression for load applied y = x10-2mE = N/m2

RESULT

Youngs modulus of the material

of the beam (metre scale) = newton/metre2

DETERMINATION OF BAND GAP IN A SEMICONDUCTOR USING A REVERSE BIASED pn-DIODE

Expt. No:

Date:

AIM

To find the width of the forbidden energy gap in a semiconductor material taken in the form a pn diode.

APPARATUS REQUIRED

1. 0 15 v dc power supply

2. Heating arrangement to heat the diode

3. Thermometer (0C to 100C)

4. Micrometer (0 50 A)

5. Germanium diode.

FORMULA

The width of the forbidden energy gap is given by Eg = 0.198 x slope eVCircuit:

The circuit diagram for conducting the experiment is shown in fig. 6.1. The diode is reverse biased with the help of dc voltage obtained from a dc power supply and the current that flows through the reverse biased diode is measured with a micrometer. A heating system (heating coil or oil bath) helps to raise the temperature of the diode. The circuit is available in a ready-to-use training board form also.

PROCEDURE

Sufficiently long wires are soldered to the diode terminals and diode is connected in to the circuit as shown in fig.6.1. The diode is immersed in an oil bath which in turn is kept in a heating mantle. A thermometer is also kept in the oil bath such that its mercury bulb is just at the height of the diode. The power supply is switched on and the voltage is adjusted to say 5 volts. The current through diode and room temperature are noted. The power supply is switched off. The heating mantle is switched on and the oil bath is heated up to 65C.

Reading of temperature vs. reverse saturation current Sl.No.Temperature (T)

(C)Temperature (T)

(K)

(K-1)Resistance

()

log RT()

P

()

Q

()

R

()

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

The heating mantle is switched off when the temperature of oil bath reached 65C. The oil is stirred and time is allowed. The temperature of oil bath stabilized say at 75C. The power supply is again switched on and the voltage is kept at 5V. The temperature (say 75C) and corresponding current through the diode are noted. The oil bath is allowed to cool slowly. As its temperature falls, the current through the diode decreases. As the current falls through steps of 2 A the corresponding temperatures are noted down in the table. The calculations are completed. A graph is plotted taking on X axis and log Io on Y axis. A straight line such fig.6.2 is obtained. The slope of the straight line is determined and using it in the formula, the band gap Eg calculated.

VIVA VOCE 1. Define Fermi level.

Fermi level is that state at which the probability of electron occupation is at any temperature above 0K and also it is the level of maximum energy of the filled states at 0K.

2. What are intrinsic semiconductors? Give examples.

Intrinsic semiconductors are semiconductors in pure form. These materials are having an energy gap of the order of 1 eV. Charge carriers are generated due to breaking of covalent bonds. Geand Si are some examples of intrinsic semiconductors.

3. What are extrinsic semiconductors? Give examples.

A semi conducting material in which the charge carriers originate from impurity atoms added to the material is called extrinsic semiconductor. The addition of impurity increases the carrier concentration and hence the conductivity of the conductor.

Phosphorous, arsenic or antimony added to either germanium or silicon gives n-type semiconductors, while aluminums, gallium or indium added results in p-type semiconductors.

RESULT

The width of the forbidden gap in germanium semiconductor is = ------------eVALL THE BEST

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Documents

Lab Manual