PHY/II/02 Student's Copy
2 0 1 8
Pre-CBCS
2nd Semester
PHYSICS
SECOND PAPER
Oscillations, Acoustics and Optics
Pre-revised
Full Marks 55
Time 2½ hours
PART A—OBJECTIVE
Marks 20
The figures in the margin indicate full marks for the questions
SECTION—A
Marks 5
Tick the correct answer in the brackets provided 1×5=5
1. In CRO, the deflection of electrons by two mutually perpendicular electric
fields with the same amplitude and having 90° phase difference results
in electron path which is a/an
ellipse
parabola
circle
straight line
/374 1 Contd.
2. The persistent audible sound after the source is cut off due to successive
reflections from the walls of an enclosure is called
echo
reverberation
resonance
intensity
3. The basic reason for chromatic aberration of a lens is
different wavelengths of light have different refractive indices
different wavelengths of light have the same refractive indices
different wavelengths of light have the same colours
different wavelengths of light have different colours
4. In Fresnel biprism interference patterns are formed due to
two real sources located at same lateral distances from the axis of
the lenses
two virtual sources due to reflection of light at the biprism
two virtual sources due to refraction of light at the biprism
two real sources due to reflection of light at the biprism
5. Polarization phenomena is observed in light wave because they are
having specific wavelength and frequency
waves those can travel long distances without altering their
wavelength
longitudinal waves
transverse waves
PHY/II/02 2 Contd.
SECTION—B
Marks 15
Give very short answers to the following questions 3×5=15
1. What are standing waves?
2. What are sound intensity and loudness? How are they different?
3. What are axial and lateral chromatic error?
4. What are Fresnel half-period zones?
5. Explain double refraction.
PART B—DESCRIPTIVE
Marks 35
The figures in the margin indicate full marks for the questions
1. Show that the total energy of a particle in simple harmonic motion is
conserved. 3
Derive an expression for the time period of oscillation of a bar
pendulum. 4
OR
Considering only the effect of gravity, show that the speed of gravity wave
over a liquid surface is given by v gl
2p
where g is acceleration due to
gravity and l is the wavelength of the wave. 7
PHY/II/02 3 Contd.
2. Show that in forced vibration, the resultant amplitude is given by
where f is external force per unit mass, w is natural angular frequency, b is
damping coefficient and p is external angular frequency. 7
OR
Obtain the expression for the growth of energy density in an enclosure
(room) of volume V . 7
3. What are aplanatic points and aplanatic surface? Discuss the principle
of Abbe's homogeneous oil-immersion microscopic objectives.
OR
What are cardinal points? Obtain the positions of cardinal points in
Ramsden's eyepiece.
4. Explain the formation of interference fringes in Michelson interferometer.
Discuss how it can be used for determination of wavelength.
OR
Explain diffraction at N slits. Give the theory of plane transmission grating
and explain how it is used to determine the wavelength of light. 7
5. State and explain Brewster's laws for polarization of light. What is optical
rotation? Explain the production of polarized light by reflection.
OR
What are spontaneous and stimulated emissions? What are the
conditions for laser action?
Explain Faraday effect. 3