Cse physics Lab Manual

7/29/2019 Cse physics Lab Manual

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TKRCET ENGINEERING PHYSICS LAB

INDEX

S.NO NAME OF THE EXPERIMENT

DATE OF

CONDUCTINGEXPERIMENT

1. RC CIRCUIT

2. BENDING LOSSES IN FIBERS

3. DIFFRACTION GRATING

4. DISPERSION OF LIGHT

5. ENERGY GAP OF A SEMICONDUCTOR

6. LCR CIRCUIT

7. MELDES EXPERIMENT

8. NUMERICAL APERTURE OF OPTICAL FIBERS

9. NEWTONS RINGS

10. PARALLEL FRINGES

11. SINGLE SLIT DIFFRACTION USING LASERS

12. STEWART & GEES METHOD

13. TORSIONAL PENDULUM


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RC CIRCUIT

AIM: To study charging and discharging of a series RC circuit and to determine the time

constant.

APPARATUS:

a) Equipment: RC Circuit Trainer Kit, Connecting Wire, Power Supply etc.,b) Instruments: Ammeter, Voltmeter, Stop Clock etc.,

CIRCUIT DIAGRAM:

INTRODUCTION & DESCRIPTION:

A capacitor is a device which can store electric charge. The ability of a capacitor to holdelectric charge is known as the capacity of a conductor. Different conductors at the same

potential can have different capacities for holding electric charge-depending on their size and

shape. The capacity or the capacitance of a conductor may be defined as the charge required

raising its potential by unity. The unit of capacitance is farad (F).

In an electric circuit, when a capacitor and a resistor are connected in series as shown in

the circuit diagram, electric charges build up across the capacitor. The discharge of the condenser

takes place when the circuit is disconnected from the source of power supply.

Let us consider a capacitor C is connected in series to a resistor of resistance R and is

being charged by using a battery of e.m.f E. When the power supply is ON, the capacitor begins

to acquire charge. Initially, the current through he circuit is high and the potential difference

across it is zero. During charging, the potential difference across the capacitor increases while

the current through the circuit decreases. When the capacitor is fully charged, there is no current

passing through the circuit and the potential difference across the capacitor is maximum and is

same as that of the applied potential difference V.

RESET

R

C

V


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THEORY: When the voltage V is applied to a capacitor in series with a resistor, transient

current flows through the circuit as the capacitor is charging. The current drops to zero when the

capacitor is fully charged.

During Charging:

From the Circuit Diagram,

At any instant of time t, the potential difference between the plates will be q/C. But this

acts opposite to the applied e.m.f E. So the effective e.m.f. is given by,

E - q/C.

According to Ohms Law, the e.m.f. will be equal to iR.

E q/C = iR -------------1

Let q0 be the maximum possible charge on the plates of condenser, then,

/ Equation 1 can be written as

.

1 .

Integrating on both sides

1 .

l n Where A = Integrating constant.

When t=0 ; q=0 then

0 l n


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l n

ln

/

1

1

1

The above equation can be written interms of voltage across the capacitor as

1

When

1

1 1

1 12.7180.63 63%

The time constant is defined as the time taken for the capacitor to charge to 63%of its maximum value.

OR

The time taken for the voltage across the capacitor becomes 63% of its maximum value.


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The variation of voltage with time is as shown in figure.

Time in seconds

Voltage


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Table-1: Charging

R = C = F

S.NO TIME in seconds VOLTAGE in volts CURRENT in amperes


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During Discharging:

When the battery is disconnected from the circuit then

0

1 .

Integrating on both sides

1 .

ln q where B=Integration constant

0 ;

ln

In terms of voltage across the capacitor,

,

0.37 37% The time taken for the voltage across the capacitor becomes 37%of its maximum value is

known as time constant.


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V0

VOLTAGEinv

olts

TIME in seconds

0.37V0

The variation of voltage with time is as shown in figure:


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Table-1: Discharging

R = C = F

S.NO TIME in seconds VOLTAGE in volts CURRENT in amperes


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PROCEDURE:

1. Connect the circuit as shown in the circuit diagram.2. Switch the power supply ON and switchover the contact to charging position.3. Press the Reset button once and start taking Ammeter & corresponding Voltmeter

readings at regular intervals using stop clock or timer and the readings are tabulated.4. Now, switch over the contact to discharging position and note down the ammeter &

voltmeter readings at regular intervals and the readings are tabulated.

5. The time constant is measured in both charging & discharging position and the results arecompared both experimentally and graphically.

RESULT:

During Charging The time constant experimentally =

The time constant graphically =

During Discharging - The time constant experimentally =

The time constant graphically =

VIVA VOCE:

1. Define the charging time of a capacitor.2. Why a resistance of low value id not acceptable in charging process?3. What will happen if the resistance of low value is connected in the circuit?4. State four types of capacitors.5. Give the applications of capacitors.6. State the factors affecting capacitance.


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TABLE:

VOLTAGE = volts

Temperature

t 0C

T = t + 273

K

Current

I AR = V/I log 10 R

1/T

K


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OBSERVATIONS:

1. Mass of the String (Thread) = w = .gm2. Length of the (thread) string = y = .cm3. Linear density of the thread = w/y = .gm/cm4. Mass of the card board pan = m = ..gm

TABLE 1: TRANSEVERSE ARRANGEMENT

S.NO

Load applied

into the panM gm

Tension

T=(M+m)gdynes

No.of

Loopsx

Length of

x loopsd cm

Length of

each loopl=d/x cm

Average =

The average value of

is substituted in equation (1) and the frequency of the fork or vibrator isdetermined.


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TABLE 2: LONGITUDINAL ARRANGEMENT

S.NOLoad appliedinto the pan

M gm

TensionT=(M+m)g

dynes

No.ofLoops

x

Length ofx loops

d cm

Length ofeach loopl=d/x cm

Average =

The average value of

is substituted in equation (2) and the frequency of the fork or vibrator isdetermined.


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Cse physics Lab Manual