Optics Answers

20 Which of the following is NOT correct?
a. light is a longitudinal wave

b. light is a tranverse wave

c. light is an electromagnetic wave

d. light can exhibit the phenomenon of polarisation

21 Light is a form of energy that -------

a. is transported from place to place due to the temperature gradient
b. requires material media for its propagation
c. stimulates the sensation of sight
d. cannot be difrracted

16 How far from a magnifying glass do you place an object to view it?
a. closer than than the focal length
b. distance equal to the focal length
c. greater than the focal length but less than twice the focal length
at twice the focal length
d.at twice the focal length
17 Telescopes that use mirrors as the objectives are known as -----------
a. refractors
b. reflectors
c. Galilean telescopes
d. terrestial telescopes
18 The property of light waves that detrmines its brightness is its -----------
a. wavelength
b. velocity
c. frequency
d. amplitude
19 The speed of light in glass is approximately ---------- that in air
a. 100 times faster than
b. 100 times slower than
c. 50 per cent faster than
d. 33 percent slower than

11 What type of image is formed when an object is placed at a distance of 1.5 focal lengths from a convex mirror?
a. erect and virtual
b. inverted and virtual
c. erect and real
d. inverted and real

12 Where is the image located when an object is 60 cm from a convex mirror with a focal length of20 cm?
a. 15 cm behind
b. 30 cm behind
c. 60 cm behind
d. 15 cm in front

13. If the sun is 150 million km away from the earth, how long does it take sunlight to reach the earth
a. 0.5 s
b. 1500 s
c. 45 s
d. 500 s
14 The critical angle for total internal reflection at an air-water interface is approximately 48 degrees. In which of the following situations will total internal reflection occur?
a. light incident in water at 40 dgrees
b. light incident in water at 55 dgrees
c. light incident in air at 40 dgrees
d. light incident in air at 55 dgrees
15 How many diopters are there for for a converging lens with a focal length of 0.4m?

a. −2.5
b. −0.4
c. +0.4
d. +2.5

5. If you stand 2 m in front of a plane mirror, how far from you is your image
a. 1 m

b. 2 m

c. 3 m

d. 4 m
6. If a 4-m-tall child stands 2 m in front of a vertical plane mirror, the image of the child will be ------- m tall
a. 1

b. 2

c. 3

d. 4
7. If rays of light parallel and close to the principal axis are incident on a --------- mirror, they converge to a point after reflection from the mirror
a. plane

b. convex

c. concave

d. diffuse

8 What type of mirror would you use to produce a magnified image of your face?
a. plane

b. concave

c. convex

d. diffuse

9 The focal length of a curved mirror is -------- the radius of the spherical surface.
a. twice
b. equal to
c. half
d. one-quater

10 The image formed by a bathroom mirror is
a. erect and virtual
b. erect and real
c. inverted and virtual
d. inverted and real

1 .The critical angle for total internal reflection at an air-water interface is approximately 48o
. In which of the following situations will total internal reflection occur?

a. light incident in water at 40o
b. light incident in water at 55o
c.light incident in air at 40o
d. light incident in air at 48o

2 What effect does enlarging of the hole in a pinhole camera have on the image? The image gets

a. larger

b smaller

c. shaper

d. fuzzier

3. A camera obscura used by a potrait painter is located 6 m from a child who stands 1 m tall. How tall is her image if the back of the camera obscura is 2 m away?

a. 1/3 m

b. 1/2 m

c 1 m

d 3 m

4 The law of reflection states that
a. light travels in a straight line
b. light must be reflected into our eyes to be seen
c. the angle of reflection is equal to the angle of incidence
d. light striking a rough surface is scattered in all directions

A He-Ne laser emits a beam of diameter 2×10−3m and wavelength 630 nm. It is directed
towards an aeroplane flying at a height of 11 km. Calculate the diameter of the light patch
produced on the surface of the aeroplane

Show that: 1) u = e^x sin y is a solution of Laplace's equation.
2) u = x^2 + t^2 is a solution of the wave equation.

1.
a) Consider a wave represented as y(x, t) = 2sin(10(3.14*t)-3.14*x/40+3.14/4).Plot the space profile at t = T/4 and time profile at x = lemda/8.
b) Describe polarization of light by double refraction. Draw o- and e- wave surfaces for
calcite and quartz.
c) Explain the concept of population inversion on the basis of Einstein’s A & B coefficients.
Discuss its significance for developing a LASER.
d) What is a zone plate? Show that it acts as a multi-foci converging lens.
e) Discuss the concept of missing orders with particular reference to double slit diffraction
pattern.

5.
a) Discuss three important practical applications of lasers.

b) Calculate the ratio of stimulated emission and spontaneous emission at an operating
temperature of 1100 K, if the wavelength of emitted light is 550 nm. Do these conditions
correspond to a laser?

c) State the characteristics of different types of optical fibres. Depict their refractive index
profiles and propagation of light through them.