PHY/II/02 Student's Copy
2 0 1 8
Pre-CBCS
2nd Semester
PHYSICS
SECOND PAPER
Oscillations, Acoustics and Optics
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. The time period T of a simple pendulum of length l is given by
2. A musical scale extends over about seven octaves from a pitch of
4 to 40 40 to 400
40 to 4000 400 to 4000
/375 1 Contd.
3. Ramsden's eyepiece is better than Huygens' eyepiece for the correction of
coma distortion
curvature astigmatism
4. In which phenomena, a plane polarized light is passed through substance
of high refractive index placed in a strong magnetic field such that the
direction of the incident light is rotated?
Brewster's law
Faraday effect
Polarization of light
Double refraction
5. The separations between the lines in sodium spectrum are
D1
=5896 ´10-8 cm and D2
5890 ´10-8 cm; the resolving power of
the arrangement is approximately equal to
9 × 82 ´102 9 × 82 ´103
9 × 82 ´104 9 × 82 ´105
SECTION—B
Marks 15
Write very short answers to the following questions 3×5=15
1. What are Lissajous figures? Draw the different patterns of the figures.
2. The intensity of a sound is 10-10 watt/cm2. If the threshold intensity
is 10-12 watt/m2, calculate the intensity level of sound in dB.
3. What are aplanatic points and aplanatic surfaces?
4. In Newton's ring experiment, the diameter of mth dark is 8 mm and
the diameter of 5)th dark ring is 12 mm. If the radius of the lower
surface of the lens is 10 find the wavelength of the light used.
5. What do you mean by the diffraction of light? Distinguish between
Fresnel's and Fraunhofer's type of diffraction.
PHY/II/02 2 Contd.
PART B—DESCRIPTIVE
Marks 35
The figures in the margin indicate full marks for the questions
1. What is a compound pendulum? Derive an equation for time period
in a compound pendulum T I
mgl
2p where I g and l have their
usual meanings. 4
Write the advantages of compound pendulum over a simple pendulum. 3
OR
What are standing waves? Explain with diagram the formation of nodes
and antinodes in standing waves.
Explain Chladni's figures with suitable diagram. 3
2. What is a free vibration? Deduce an equation for frequency of free
vibration.
State and explain Sabine's law for reverberation time. 3
OR
Discuss the method for the production of ultrasonic waves. 3
What are the features of ultrasonic waves? Explain the important
application of the waves.
3. Derive an expression for the condition of achromatic combination of two
lenses separated by a distance d. Discuss the condition for lateral
achromatism.
OR
What are the different cardinal points in a thick lens? 2
Find the distances of cardinal points of first principal from the centre
of first lens and first focal point from first principal point in Huygens'
eyepiece. 5

4. What is interference of light? 2
Explain the construction and working of Michelson interferometer
with suitable diagram and derive an equation for determining the
difference of wavelength emitted from closed sources of light.
OR
What is polarization of light? Explain the production of polarized light
by the method of reflection of light.
State and explain Brewster's law. 2
5. Define zone plate. 2
With suitable diagram, show that the area of each of the Fresnel's
half-period zones is pbl, where b is the distance of the point from the
pole of the wavefront and the wavelength of the light. 5
OR
Discuss the single slit experiment in Fraunhofer's diffraction and
obtain the conditions for maxima and minima intensities of light. 4
Define the resolution of images and explain the Rayleigh criterion for
the resolution of images.