CBSE
Multiple Choice QuestionsA plano-concave lens is made of glass of refractive index 1.5 and the radius of curvature of its curved face is 100 cm. What is the power of the lens ?
+ 0.5 D
− 0.5 D
− 2 D
+ 2 D
The intermediate image formed by the objective of a compound microscope is
real, inverted and magnified
real, erect and magnified
virtual, erect and magnified
virtual, inverted and magnified
A plano-convex lens fits exactly into a plano-concave lens. Their plane surfaces are parallel to each other. If lenses are made of different materials of refractive indices µ1 and µ2 and R is the radius of curvature of the curved surface of the lenses, then the focal length of the combination is
A glass slab consists of thin uniform layers of progressively decreasing refractive indices RI (see figure) such that the RI of any layer is µ − m Δµ. Here, µ and Δµ denote the RI of 0th layer and the difference in RI between any two consecutive layers, respectively. The integer m =0, 1, 2, 3, ... denotes the numbers of the successive layers. A ray of light from the 0th layer enters the 1st layer at an angle of incidence of 30°. After undergoing the mth refraction, the ray emerges parallel to the interface. If µ = 1.5 and Δµ = 0.015, the value of m is
20
30
40
50
A luminous object is separated from a screen by distance d. A convex lens is placed between the object and the screen such that it forms a distinct image on the screen. The maximum possible focal length of this convex lens is
4d
2d
An object placed in front of a concave mirror at a distance of x cm from the pole gives a 3 times magnified real image. If it is moved to a distance of (x + 5) cm, the magnification of the image becomes 2. The focal length of the mirror is
15 cm
20 cm
25 cm
30 cm
For a normal eye, the cornea of eye provides a converging power of 40 D and the least converging power of the eye lens behind the cornea is 20 D. Using this information, the distance between the retina and the cornea-eye lens can be estimated to be
5 cm
2.5 cm
1.67 cm
1.5 cm
If the velocity of light in vacuum is 3 x 108 ms-1, the time taken (in nanosecond) to travel through a glass plate of thickness 10 cm and refractive index 1.5 is
0.5
1.0
2.0
3.0
An object is located 4 m from the first of two thin converging lenses of focal lengths 2 m and 1 m, respectively. The lenses are separated by 3 m. The final image formed by the second lens is located from the source at a distance of
8.0 m
5.5 m
6.0 m
6.5 m
An object is placed 30 cm away from a convex lens of focal length 10 cm and a sharp image is formed on a screen. Now a concave lens is placed in contact with the convex lens. The screen now has to be moved by 45 cm to get a sharp image again. The magnitude of focal length of the concave lens is (in cm)
72
60
36
20
