5. Differentiate between Phase and Group velocities.
Given that phase velocity V of waves in
deep water is (g l /2p ) 1/2 ,find their group velocity v. (20)
6. What is interferometer? Describe the construction and working principle of an
interferometer with which you are familiar. (20)
Q3. (a) What is meant by Interference of Light? Also distinguish between Constructive
Interference and Destructive Interference.
(b) Derive an expression for the Resolving Power of a plane diffraction grating.
(c) Monochromatic light emitted from He-Ne laser source with λ = 632.8 nm is incident
normally on a diffraction grating containing 6000 lines per cm. Find the angles at which one
would observe the first order maximum and the second order maximum. Will it be possible to
observe the third order maximum as well?
Q4. (a) Differentiate between Travelling Waves and Standing Waves.
(b) Prove that the Rate of Transfer of Energy in wave motion depends on the square of the
wave amplitude and square of the wave frequency. (marks 10)
(c) Spherical waves travel from a source of waves whose power output, assumed constant, is P.
What will be the wave intensity I at a distance from the source?
Laser and its Applications
Q.4 Write the general equation for „damped harmonic oscillator.‟ Solve it and discuss all the
three features of damping i.e. when damping is small, medium, and high.
Q.5 (a) What is interference of light? What are the necessary conditions for interference? (b)
How interference pattern is formed in case of Newton‟s Rings? Drive an expression for the
radius of the dark and bright fingers.
Standing Waves
Q.4. (a) What is simple harmonic motion (SHM)? Write the equation for SHM and solve it to
find it‟s time period. (2,4,8)
(b) A body oscillates with SHM according to equation: (6) x=(6.12m)cos(8.38 rad/s)t+1.92 rad.
Find its time period.
Q.5. (a) What do you understand by diffraction of light? Give all the necessary conditions.
Explain diffraction through a single slit and derive an expression for the minimas in the
diffraction pattern. (2,4,4,6)
(b) Monochromatic light of wavelength 44lnm falls on a narrow slit On screen 2.16m away, the
distance between the second minima and the central maxima is 1.62cm. Find the width of the
slit. (4)
Laser and its applications
Q.6. (a) What is Polarization of light? Explain Polarization by reflection and obtain Brewster
Law.
Also explain the idea of double refraction. (13)
(b) We wish to use a Quartz sheet (n=1.54) in air as polarizer. Find the polarizing angle and
angle
of refraction. (05)
(c) Why can't we polarize sound waves?
Q.6. (a) Differentiate between the phase velocity and the group velocity. Sound waves can be
used to measure the speed at which blood flows in artries and veins. Explain how?
(b) Use Maxwell’s equations to derive the electromagnetic wave equation. (10)
Travelling waves and standing waves
Q. 3. (a)
State Hook’s Law. A mass attached to an elastic spring is displaced from its
equilibrium position and released. Show that its motion is simple harmonic and
derive the differential equation, relation for instantaneous velocity, displacement
and acceleration and plot each quantity with time for such motion.
A block of unknown mass is attached with an elastic spring having spring
constant 6.5N/m and undergoes simple harmonic motion with an amplitude of 10
cm. When the block is half way between its equilibrium position and end point, its
speed is 30cm/sec. Find
(i) Mass of the block (ii) Time period of the system
(iii) Maximum acceleration of the block
A mass spring system is in an elevator which moves upward with an acceleration
“a”. What will be the effect on measured value of spring constant compared to its
value when elevator is at rest.
Q.No.4. (a) What is Doppler’s effect? Derive expressions of frequency of sound heard by
observer when:
(i) The observer moving towards a stationary source
(ii) The source is moving towards a stationary observer.
(b) A stationary observer detects sound of frequency 250 hertz emitted from a source
at rest. He detects sound of frequency 750 hertz when source is moving towards
him with constant velocity. Determine velocity of sound.
(Velocity of sound = 341 m/Sec.)
Q.No.5. (a) Describe the Young’s double slit experiment and find the conditions of
constructive and destructive interference.
(b) The double slit arrangement is illuminated by light of wavelength 546nm, the
slits are 0.12mm apart and the screen on which the interference pattern appears is
55cm away. What is angular position of first maxima? What is linear distance
between 3rd and 4th maxima?
(a) Travelling and Standing Waves.
(b) LASER, its production and applications.
