A point object O is placed at distance 20 cm from a biconvex lens of radius of curvature 20 cm and =1.5. The final image produced by lens and mirror combination will be at
(1) 10 cm from the mirror
(2) 20 cm from lens
(3) -20 cm from lens
(4) -15 cm from the mirror
If the angle of a triangular prism is A and the refractive index of the material is , then under what condition will there be no emergent ray?
1.
2.
3.
4.
A thin lens whose power is +2D is cut into two pieces perpendicular to the principal axis. The focal length of each part will be
(1) 1 m
(2) 0.1 m
(3) 75 cm
(4) 0.05 m
A light ray is incident at an angle of on one face of a prism of a refractive angle . If light ray grazes the second face, then the refractive index of the material of prism is-
1.
2.
3.
4.
The near point of a hypermetropic eye is 1m. What is the power of the lens required to correct this defect?
(1) -3 D
(2) +3 D
(3) +1 D
(4) -1.75 D
The minimum magnifying power of an astronomical telescope is 40. If the length of the telescope is 205 cm, then the focal length of its field lens is:
1. 5 cm
2. 200 cm
3. 40 cm
4. 140 cm
A boy with defective eye-sight cannot see things beyond 50 cm. The corrective lens required has the power:
1. +1 D
2. +2 D
3. -1 D
4. -2 D
The focal lengths of the objective and eyepiece of a terrestrial telescope are 50 cm and 10 cm respectively. The magnifying power of the telescope when the final image is formed at infinity is
(1) 3.75
(2) -2.5
(3) -4.25
(4) +5
A convex mirror of focal length \(20\) cm forms an image that is quarter of the object's size. The distance of the object from the mirror is:
1. \(50\) cm
2. \(-60\) cm
3. \(-40\) cm
4. \(-70\) cm
The focal length of a thin convex lens for red and blue light is 0.5m and 0.484m. The dispersive power of the lens is
1. 0.984
2. 0.032
3. 0.484
4. 0.434