CBSE
Multiple Choice QuestionsIf the focal length of the eye-piece of a telescope is doubled, its magnifying power (m) will be
2 m
3 m
4 m
A plano-convex lens (f = 20 cm) is silvered at plane surface. Now focal length will be
20 cm
40 cm
30 cm
10 cm
Two mirrors at an angle 0° produce 5 images of a point. The number of images produced when θ is decreased to θ − 30° is
9
10
11
12
A beam of monochromatic blue light of wavelength 4200 in air travels in water of refractive index 4/3. Its wavelength in water will be.
4200
5800
4150
3150
A convex lens of focal length 30 cm produces 5 times magnified real image of an object. What is the object distance?
36 cm
25 cm
30 cm
150 cm
A 2.0 cm object is placed 15 cm in front of a concave mirror of focal length 10 cm. What is the size and nature of the image ?
4 cm, real
4 cm, virtual
1.0 cm, real
None of these
If x1 be the size of the magnified image and x2 the size of the diminished image in Lens Displacement Method, then the size of the object is
x1x2
x12x2
x1x22
Two thin lenses of focal lengths 20 cm and 25 cm are placed in contact. The effective power of the combination is
9 D
2 D
3 D
7 D
The radius of the light circle observed by a fish at a depth of 12 m is (refractive index of water = 4/3)
Short Answer TypeA ray of light travelling inside a rectangular glass block of refractive index is incident on the glass-air surface at an angle of incidence of 45°. Show that the ray will emerge into the air at an angle of refraction equal to 90°.
