Ray Optics and Optical Instruments

In a concave lens, a ray of light emanating from the object parallel to the principal axis of the lens, after refraction :

1. passes through the second principal focus.
2. appears to diverge from the first principal focus.
3. passes through 2F, which is the radius of curvature of the lens.
4. emerges parallel to the principal axis.

A ray of monochromatic light is passing through an equilateral prism (ABC) as shown in the figure. The refracted ray (QR) is parallel to its base (BC) and the angle of incidence (i) is 50°. Then the angle of deviation (δ) is : [figure]

1. 45°
2. 55°
3. 35°
4. 40°

Consider three media P, Q and R with refractive indices 1, 1.25, and 1.5 respectively. The medium Q having a thickness of 5 cm is placed between extended media P and R as shown in the figure. An object O is placed at the centre of medium Q. If viewed from medium P near the normal direction, the apparent depth of O is h1. For similar observation from medium R, the apparent depth is h2. The value of |h1 - h2|, in cm, is: [figure]

1. 3
2. 0
3. 1
4. 2

The lens combination as shown in the figure, consists of two lenses, L1 and L2, of the focal lengths +10 cm and -10 cm, respectively. The position of the image formed is: [figure]

1. 60 cm to the right of the concave lens
2. 20 cm to the left of the concave lens
3. 60 cm to the left of the concave lens
4. 30 cm to the right of the concave lens

A microscope has an objective of focal length 2 cm, eyepiece of focal length 4 cm and the tube length of 40 cm. If the distance of distinct vision of eye is 25 cm, the magnification in the microscope is

1. 150
2. 250
3. 100
4. 125

In a certain camera, a combination of four similar thin convex lenses are arranged axially in contact. Then the power of the combination and the total magnification in comparison to the power (p) and magnification (m) for each lens will be, respectively

1. 4p and m4
2. p4 and m4
3. 4p and 4m
4. p4 and 4m

A light ray enters through a right angled prism at point P with the angle of incidence 30 as shown in figure. It travels through the prism parallel to its base BC and emerges along the face AC. The refractive index of the prism is: [figure]

1. 54
2. 52
3. 34
4. 32

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

A convex lens 'A' of focal length 20 cm and a concave lens 'B' of focal length 5 cm are kept along the same axis with a distance 'd' between them. If a parallel beam of light falling on 'A' leaves 'B' as a parallel beam, then the distance 'd' in cm will be :

1. 30
2. 25
3. 15
4. 50

A lens of large focal length and large aperture is best suited as an objective of an astronomical telescope since :

1. a large aperture contributes to the quality and visibility of the images.
2. a large area of the objective ensures better light gathering power.
3. a large aperture provides a better resolution.
4. All the above.

A point object is placed at a distance of 60 cm from a convex lens of focal length 30 cm. If a plane mirror were put perpendicular to the principal axis of the lens and at a distance of 40 cm from it, the final image would be formed at a distance of - [figure]

1. 20 cm from the plane mirror, it would be a virtual image.
2. 20 cm from the lens, it would be a real image.
3. 30 cm from the lens, it would be a real image.
4. 30 cm from the plane mirror, it would be a virtual image.

A ray is incident at an angle of incidence i on one surface of a small angle prism (with angle of prism A) and emerges normally from the opposite surface. If the refractive index of the material of the prism is , then the angle of incidence is nearly equal to :

1. 2A
2. A
3. A2
4. A2

In total internal reflection when the angle of incidence is equal to the critical angle for the pair of media in contact, what will be angle of refraction?

1. equal to angle of incidence
2. 90
3. 180
4. 0

Pick the wrong answer in the context with rainbow.

1. An observer can see a rainbow when his front is towards the sun.
2. Rainbow is a combined effect of dispersion, refraction and reflection of sunlight.
3. When the light rays undergo two internal reflections in a water drop, a secondary rainbow is formed.
4. The order of colours is reversed in the secondary rainbow.

Two similar thin equi-convex lenses, of focal length f each, are kept coaxially in contact with each other such that the focal length of the combination is F1. When the space between the two lenses is filled with glycerin (which has the same refractive index ( = 1.5) as that of glass) then the equivalent focal length is F2. The ratio F1 : F2 will be :

1. 1 : 2
2. 2 : 3
3. 3 : 4
4. 2 : 1

The refractive index of the material of a prism is 2 and the angle of the prism is 30 . One of the two refracting surfaces of the prism is made a mirror inwards, by silver coating. A beam of monochromatic light entering the prism from the other face will retrace its path (after reflection from the silvered surface) if its angle of incidence on the prism is

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

An object is placed at a distance of 40 cm from a concave mirror of focal length 15 cm. If the object is displaced through a distance of 20 cm towards the mirror, the displacement of the image will be

1. 30 cm away from the mirror
2. 36 cm away from the mirror
3. 30 cm towards the mirror
4. 36 cm towards the mirror

An astronomical refracting telescope will have large angular magnification and high angular resolution, when it has an objective lens of

1. small focal length and large diameter
2. large focal length and small diameter
3. large focal length and large diameter
4. small focal length and small diameter

A beam of light from a source L is incident normally on a plane mirror fixed at a certain distance x from the source. The beam is reflected back as a spot on a scale placed just above the source L. When the mirror is rotated through a small angle , the spot of the light is found to move through a distance y on the scale. The angle is given by

1. yx
2. x2y
3. xy
4. y2x

A thin prism having refracting angle 10 is made of glass of refractive index 1.42. This prism is combined with another thin prism of glass of refractive index 1.7. This combination produces dispersion without deviation. The refracting angle of second prism should be

1. 6
2. 8
3. 10
4. 4

An astronomical telescope has objective and eyepiece of focal lengths 40 cm and 4 cm respectively. To view an object 200 cm away from the objective, the lenses must be separated by a distance

1. 50.0 cm
2. 54.0 cm
3. 37.3 cm
4. 46.0 cm