Two convex lenses of focal length X and Y are placed parallel to each other. An object at infinity from the first lens forms its image at infinity from the second lens. The separation between the two lenses should be:
1. | X + Y | 2. | \(\frac{X + Y}{2}\) |
3. | X - Y | 4. | \(\frac{X - Y}{2}\) |
A plane mirror is placed at the bottom of a fish tank filled with water of refractive index . The fish is at a height 10 cm above the plane mirror. An observer O is vertically above the fish outside water. The apparent distance between the fish and its image is:
1. 15 cm
2. 30 cm
3. 35 cm
4. 45 cm
A liquid of refractive index is placed between two identical planoconvex-lenses touching each other at their spherical surfaces of radius R. If the refractive index of the lens is 1.50, then the lens behaves as:
1. | a convergent with power \(\mathrm{P}=\frac{1}{3 R}\) |
2. | a convergent with power \(\mathrm{P}=\frac{1}{6 R}\) |
3. | a divergent with power \(\mathrm{P}=\frac{1}{3 R}\) |
4. | a divergent with power \(\mathrm{P}=\frac{1}{6 R}\) |
If there is no emergent light through a prism of refracting angle \(60^{\circ},\) whatever may be the angle of incidence, then the minimum value of the refractive index of the material of the prism is:
1. 2
2.
3. 1.5
4.
The Refractive index of material of an equilateral prism is . Angle of incidence for minimum deviation is:
1. \(60^{\circ}\)
2. \(45^{\circ}\)
3. \(30^{\circ}\)
4. \(15^{\circ}\)
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
If \(C_1,~C_2 ~\mathrm{and}~C_3\) are the critical angle of glass-air interface for red, violet and yellow color, then:
1. | \(C_3>C_2>C_1\) | 2. | \(C_1>C_2>C_3\) |
3. | \(C_1=C_2=C_3\) | 4. | \(C_1>C_3>C_2\) |
An astronomical telescope has angular magnification of 40 in its normal adjustment. If focal length of eyepiece is 5 cm, the length of the telescope is:
1. 190 cm
2. 200 cm
3. 205 cm
4. 210 cm
The focal length of a convex lens is 40 cm and the size of the inverted image formed is half of the object. The distance of the object is:
1. | 60 cm | 2. | 120 cm |
3. | 30 cm | 4. | 180 cm |