When a concave mirror of focal length f is immersed in water, its focal length becomes f', then:

1.	f'=f
2.	f'<f
3.	f'>f
4.	The information is insufficient to predict

A person cannot see objects clearly that are closer than 2 m and farther than 4 m. To correct the eye vision, the person will use:

(1) Bifocal lenses of power -3.5 D and 0.25 D

(2) Bifocal lenses of power -0.25D and 3.5 D

(3) Bifocal lenses of power -0.5D and 4.0D

(4) Bifocal lenses of power -4.0D and 0.5 D

A graph is plotted between the angle of deviation $\delta$ in a triangular prism and the angle of incidence as shown in the figure. Refracting angle of the prism is: 

 
1. \(28^\circ\)
2. \(48^\circ\)
3. \(36^\circ\)
4. \(46^\circ\)

Minimum distance between real object and image produced by a concave mirror of focal length 20 cm is:

(1) 80 cm

(2) zero

(3) 20 cm

(4) 40 cm

Three lenses A, B and C are shown in the figure. Lens A is concave lens. B and C are plano-convex lenses. All the lenses have same focal length f. In which case the spherical; aberration is minimum?

1.  A

2.  B

3.  C

4.  All of the above

A small air bubble is present exactly at the centre of a glass sphere. Size of the image as seen from outside is of

(1) Same size

(2) Bigger

(3) Smaller

(4) May be smaller or bigger depending on the distance of observer

Three identical thin convex lenses are kept as shown in the figure. A ray passing through the lenses is shown. The focal length of each lens is 

1.  5 cm

2.  10 cm

3.  15 cm

4.  20 cm

An object is at a distance of 30 cm in front of a concave mirror of focal length 10 cm. The image of the object will be:

To a diver inside water, the setting sun will appear at an angle (with the horizontal) of: \(\left[ \mu_w = \frac{5}{4} \right]\)

1. \(53^{\circ}\)$$

2. \(37^{\circ}\)$$

3. \(45^{\circ}\)$$

4. \(60^{\circ}\)$$

In normal adjustment, the angular magnification of an astronomical telescope is 39. If the length of the tube is 2 m, then the focal length of the objective and eyepiece are respectively,

(1) 195 cm, 5 cm

(2) 190 cm, 10 cm

(3) 20 cm, 180 cm

(4) 10 cm, 190 cm