10-2-2014 $4 10-2-2014 $ 5
DYNAMICS
ELECGTROMAGNETIC SPECTRUM
SOUND
2.What is the principle of launching a satellite into an
orbit?(2M)A: Principle of launching a satellite:The principle of
launching an
artificial satellite into a proper space orbit is to impart
sufficientinitial horizontal speed,so that,it revolves round the
earth at thechosen height.
3. What is a centrifuge ?How does it work ?(2M)A: Centrifuge:A
centrifuge is a machine which is used to separate
particles of higher mass with those of lower mass in a given
mix-ture. Working of centrifuge:When a mixture (milk)is poured
intothe cylindrical vessel of the centrifuge and rotated with
highspeed.The particles of higher mass (skimmed milk)are thrownaway
from the centre due to greater centrifugal force and particlesof
lower mass (cream particles)get accumulated at thecentre,i.e.,near
the axle.
4. Explain the working of a laundry drier.(2M)A: Working ofa
laundry drier:In a laundry drier,the wet clothes are
dropped into a cylindrical vessel containing holes.When the
vesselis rotated,the wet clothes get stuck to the walls of the
vessel.Thecentrifugal force pushes the water molecules from the
clothes outthrough the holes.Thus,the clothes are dried.
5. Explain the characteristics of simple Harmonic Motion.(2M)A.
Simple Harmonic motion is characterised by
1)A constant time period or a constant frequency2)An amplitude
(A)and3)A constant mechanical energy which is the sum of
potentialenergy and Kinetic energy at every point in the path of
oscillation.
6. Distinguish between centripetal and centrifugal force?(4M)A:
The differences between centripetal and centrifugal forces are
given below:
5. How are X-rays produced.(2M)A. X-rays are produced in
discrete wavelengths in individual transi-
tions among the inner electrons of an atom. X-rays in
continuouswavelengths can also be produced when incident electrons
aredecelerated inside the target atoms.
6. What is meant by Radiography?(1M)A. Radiography:Medical
diagnosis,in which soft X-rays are used to
detect diseases,is called Radiography.7. What is
radiotherapy?(1M)A. Using X-rays to cure diseases is called
radiotherapy. HI Some
more important questions:8. Mention the uses of infrared
radiations.(1M)A. 1)Used in physiotherapy,
2)Used in taking photographs of objects in darkness.9. What is a
spectrum?(1M)A. A Spectrum is a group of wavelengths or
frequencies.10. Which waves are used in telemetry?(1M)A. Microwaves
are used in telemetry.11. Which is the most penetrating
electromagnetic radia-
tions?(1M)A. The most penetrating electromagnetic radiations
gamma rays.12. What information do we get from the light emitted
from the
sun?(1M)A. We get information about the composition of the
matter present in
them.13. What is the range of visible spectrum?(1M)A. The
wavelength of the visible spectrum extends from 0.4m to 0.7 14.
Which radiations are emitted by molecules when they change
their states of rotational or vibrational motion?(1M)A. Infrared
radiation.15. Which radiations are produced by the transitions of
the elec-
trons in atoms?(1M)A. Ultraviolet radiations.16. Which rays are
emitted in radioactivity?(1M)A. Gamma rays.17. How are infrared
radiations detected?(1M)A. Infrared radiations can be detected by
devices like
thermometers,thermopiles and bolometers etc.18. Mention the uses
of Microwaves.(1M)
A. 1) Microwaves are used in Radar,telemetry and microwave
ovens.2) It is also used in satellite communications.
19. What is radio -astronomy?(1M)A. Mapping of the radio
emissions from extra terrestrial sources is
known as radio astronomy.20. What is the velocity of light in
vacuum?(1M)A. The velocity of light in vacuum is 3 x 10 8 m/s.21.
How can we observe infrared radiations?(1M)A. The prisms made of
rock salt are used for observing infrared radi-
ations.22. What are electromagnetic radiations?(2M)A.
Electromagnetic radiations are characterised by oscillating
electric
and magnetic fields perpendicular to each other and
perpendicularto the direction of propagation.
23. What is the use of ozone layer in the atmosphere? (2M)A. We
are protected from uv radiations of the sun because ozone is
our atmosphere absorbs ultraviolet rays strongly. Only a little
ofthis radiation reaction the ground.
24. Mention the evil effects of ultraviolet rays?(2M)A. Brief
exposure to ultraviolet radiations causes common sun-
burn,but long term exposure can lead to skin diseases
includingcancer.
1. Distinguish between node and antinode.(2M)
A: Node:The point where the particle is at minimum displacement
orat rest,in a stationary wave is called a Node. Antinode:The
pointwhere the particle is at maximum displacement is called
anAntinode.
2. Draw a figure showing the formation of a stationary
wave.(2M)
3. What is resonating air-column?(2M)A: When a glass tube with
open ends,is immersed in water to certain
extent,the air inside the glass tube is said to form an
"aircolumn"For a particular length of this air column,a vibrating
tuningfork will give a booming sound. We call this phenomenon as
reso-nance and the air column is called resonating air column.
4. Define resonance and give examples of resonance from
day-to-day life..(4M)
A: Definition :Resonance is the phenomenon in which if one of
the twobodies of the same natural frequency is set into
vibration,the otherbody also vibrates with larger amplitude,under
the influence of thefirst body. The phenomenon of resonance is seen
in our daily life.Some of the examples are given below :
(i) Soldiers marching on the bridge: When soldiers cross a
suspen-sion bridge,they are asked to break their steps.This is
because the-frequency of vibration of their marching becomes equal
to the nat-ural frequency of the bridge.Thereby, the bridge would
vibrate witha large amplitude due to resonance and the bridge can
collapse.
(ii) Children on a swing: When children are playing on a
swing,itoscillates with large amplitude.This is because resonance
occursbetween oscillatory force applied by the person and the
natural fre-quency of the swing.
(iii) Rattling noise of cars: When a car is travelling at a
particularspeed, resonance occurs between the car-body and the
engine.Thisproduces a rattling sound.The rattling sound is not
heard when thespeed is more or less than this speed.
(iv) Perfect tuning in a radio:In a radio,you can clearly hear
the newsat one particular station because the natural frequency of
the radioresonates with the incoming signals from the radio
station.
5. Distinguish between progressive and stationary waves.(4M)
10-2-2014 $667. Describe a method to determine
the velocity of sound in air.(4M)A: To determine the velocity of
sound
in air. Apparatus required:A longglass jar,retort stand,glass
tube,tun-ing fork and a rubber hammer.Principle:It is based on the
phenom-enon of resonance of vibrating aircolumn. Experimental setup
andprocedure:Arrangement:(i)Take a long glass jar (J)of a large
diameter (about 30cms) and height (about 50 cms), (ii)Pour water
into the jaruntil 3/4 th of the jar is filled, (iii)Take another
glass-tube(T)of length 40 cms and of diameter about 3 cms,with
itsboth ends open. (iv)Fix the tube (T)to a clamp (C)of theretort
stand (R). (v)Immerse the tube (T)in the water of thejar (J)as
shown in figure.
Adjustment of length of air-column:(i)The length of the
air-column (/)as shown in figure can bevaried by raising or
lowering T using the screw (S).(ii)Adjust the position of T such
that the length of the air-column is very small. (iii)Take a tuning
fork (F)of knownfrequency (v). (iv)Strike the prongs of F with a
rubberhammer. (v)Hold the vibrating tuning fork just above
theair-column, near the tube.
set into vibration,the other body also vibrateswith larger
amplitude under the influenceof the first body.
Example: In the above figure two hollowsound boxes with one end
open arearranged such that their open ends faceeach other.Two
tuning forks 'A'and 'B'of same fre-quency are mounted on the two
boxes. Ifone of the forks C A'is set into vibrationthe fork 'B'
also begins to vibrate and a loud sound is heard.
Reason: The vibrating tuning fork 'A'vibrates the air column of
soundbox (1),which vibrates the air column of sound box (2)with the
fre-quency of A.This vibrating air column of sound box (2)excites
thetuning fork 'B 9 .Then 'B' is said to be in resonance with
'A'.
LIGHT1. What is population inversion?(1M)A: Population
inversion: The process in which the number of elec-
trons (Ns)in a higher energy state called 'meta stable state'of
anactive medium,is increased to a value greater than the number
ofelectrons (N,)in the ground state (i.e.,N2>N1), is called
'popula-tioninversion'.
2. Give differences between LASER light and ordinary light
interms of the property of 'Coherence'? (2M)
3. What are the important processes involved in the working of
alaser? (2M)
A: Basic processes involved in the working of a laser
are:(i)Absorption (ii)Spontaneous emission (iii)Pumping and
popula-tion inversion (iv)Stimulated emission of electromagnetic
radia-tion
4 . Describe a ripple tank.How does it help in understanding
thereflection of light?(4M)
A: Description of a Ripple Tank:i) Rectangular Tank:The ripple
tank essentially consists of a rec-tangle shaped trough (tank)made
of transparent glass or perspexmaterial.This tank containing water
is held at a height with thesupport of four legs.ii)Below and above
ripple tank: Below the tank,a white paper isspread on the
floor.Above the tank,a partially covered electric-bulb is fixed to
illuminate the tank.iii)At the surface of water: A small needle
(N)fixed at one end ofa metallic strip is connected to an electric
vibrator.The tip of theneedle is kept vertically in contact with
the water surface in theripple tank.
Under standing Reflection of waves through RippleTank:
i)Production of circular waves: Vibration of the needle
producescircular waves, which move forward.The origin of circular
wavesis marked as S.ii)Reflection of circular waves: When the
circular waves moveforward and hit the vertical wall of the ripple
tank they get reflect-ed and start moving in the opposite
direction.iii)Centre of reflected circular waves: These reflected
waves arealso circular in shape. The centre of the reflected waves
will be onthe other side of the wall,marked as point T.This point I
behavesas the image of the point S.(iv)Image and object distances:
The distance between the centreS of the incident wave and a point O
on the wall of the ripple tank(SO),is equal to the distance between
the centre I of the reflectedwave and a point 0 on the wall of the
ripple tank (IO).This provesthat the object distance is equal to
the image distance,as is the casein reflection of light from a
plane mirror.
5. Write the differences between Newton's corpuscular theoryand
Huygen's wave theory of light.(4M)
6. Mention the uses of lasers in medicine?(2M)A: (1)Painless
Microsurgery: Lasers are used to conduct surgeries
painlessly.(2)Treatment of diseases: (a)Liver and lung diseases
can beeffectively treated with lasers. (b)Lasers are used
extensively inthe treatment of eye-diseases,particularly to
reattach'a detachedretina. (3)Endoscopy: Lasers are used in
fibre-optics endoscopy todetect ulcers in the intestines.
7. What are the important applications of laser light in the
fieldsof science and technology?(4M)
A: Applications of Lasers:(i) Study of Atoms:
(a)Counting of atoms: The counting of atoms in a substance
hasbecome possible because of lasers.(b)Brownian motion:Lasers help
in understanding the Brownianmotion ofparticles.
(ii) Determination of rate of rotation of earth: He -Ne laser
helps indetermining the rate of rotation of the earth
accurately.
(iii) Photography: Lasers are employed in a special three
dimension-al photography called 'holography'.
(iv) Astronomy: In astronomy,lasers help in viewing far away
stellarobjects and study their nature.
(v) Micro-Raman Spectroscopy: The high intensity and
directional-ity of lasers led to the development of a new branch of
sciencecalled Mirco-Raman spectroscopy,which analyses small
quantitiesof biological and biomedical samples.
(vi)Fibre-optics communications: Lasers helped in establishing
anew revolutionary method of communications called
'fibre-opticscommunications'.
8. State and Explain the principle of superposition of
waves.(4M)A: Principle of superposition of waves: It states that
when two or
more waves travel through the same portion of a medium
simulta-neously,the resultant displacement at any point is the
vector sumof the displacements due to individual waves.
Explanation: In the case of ripple tank with two vibrating
sources,ifYj is the displacement caused at a point due to first
source and Y2 is
the displacement at the same point due to the second
source,theresultant displacement (R)at that point is given by
CURRENT - ELECTRICITY-I
