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:

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:

The condition of minimum deviation is achieved in an equilateral prism kept on the prism table of a spectrometer. If the angle of incidence is \(50^{\circ}\), the angle of deviation is:
1. \(25^{\circ}\)$$

2. \(40^{\circ}\)$$

3. \(50^{\circ}\)$$

4. \(60^{\circ}\)$$

An object is placed 20 cm in front of a concave mirror of a radius of curvature 10 cm. The position of the image from the pole of the mirror is:

1. 7.67 cm

2. 6.67 cm

3. 8.67 cm

4. 9.67 cm

The angle of minimum deviation for a glass prism of refractive index \(\mu = \sqrt{3}\) equals the refracting angle of the prism. The angle of the prism is:
1. \(30^{\circ}\)
2. \(60^{\circ}\)
3. \(90^{\circ}\)
4. \(45^{\circ}\)$$

The angle of a prism is A and one of its refracting surfaces is silvered. Light rays falling at an angle of incidence 2A on the first surface return through the same path after suffering reflection at the second (silvered) surface. The refractive index of the material is:

1.  2sinA

2.  2cosA

3.  $\frac{1}{2}$cosA

4.  tanA

The correct statement is: