Ray Optics and Optical Instruments · Question 7

A small telescope has an objective of focal length 140 cm and an eye piece of focal length 5.0 cm. The magnifying power of telescope for viewing a distant object is:

1. 34
2. 28
3. 17
4. 32

Given below are two statements: In the light of the above statements, choose the most appropriate answer from the options given below :

1. Statement I is correct but statement II is incorrect
2. Statement I is incorrect but Statement II is correct
3. Both Statement I and Statement II are correct
4. Both Statement I and Statement II are incorrect

Light travels a distance x in time t1 in air and 10x in time t2 in another denser medium. What is the critical angle for this medium?

1. -1 ( 10t2t1 )
2. -1 ( t110t2 )
3. -1 ( 10t1t2 )
4. -1 ( t2t1 )

In the figure shown here, what is the equivalent focal length of the combination of lenses (Assume that all layers are thin) ? [figure]

1. -40 cm
2. -100 cm
3. -50 cm
4. 40 cm

Two thin lenses are of same focal lengths (f), but one is convex and the other one is concave. When they are placed in contact with each other, the equivalent focal length of the combination will be :

1. f/4
2. f/2
3. Infinite
4. Zero

A biconvex lens has radii of curvature, 20 cm each. If the refractive index of the material of the lens is 1.5, the power of the lens is

1. +2 D
2. +20 D
3. +5 D
4. Infinity

Two transparent media A and B are separated by a plane boundary. The speed of light in those media are 1.5 108 m/s and 2.0 108 m/s, respectively. The critical angle for a ray of light for these two media is

1. -1(0.500)
2. -1(0.750)
3. -1(0.500)
4. -1(0.750)

During a cloudy day, a primary and a secondary rainbow may be created, then the :

1. secondary rainbow is due to single internal reflection and is formed above the primary one.
2. primary rainbow is due to double internal reflection and is formed above the secondary one.
3. primary rainbow is due to double internal reflection and is formed below the secondary one.
4. secondary rainbow is due to double internal reflection and is formed above the primary one.

An astronomical refracting telescope is being used by an observer to observe planets in normal adjustment. The focal lengths of the objective and eye piece used in the construction of the telescope are 20 m and 2 cm respectively. Consider the following statements about the telescope : The correct statements are :

1. A, B and D only
2. A, B and C only
3. B, C and D only
4. C, D and A only

Find the value of the angle of emergence from the prism. Refractive index of the glass is 3 [figure]

1. 90
2. 60
3. 30
4. 45