The images of clouds and trees in water always less bright than in reality:

1.  because water is forming the image dirty

2.  because there is an optical illusion due to which the image appears to be less bright

3.  because only a portion of the incident light is reflected and quite a large portion goes into water

4.  because the air above the surface of the water contains a lot of moisture

A convex mirror has a focal length = 20 cm. A convergent beam tending to converge to a point 20 cm behind the convex mirror on the principal axis falls on it. The image is formed at:

1.  infinity 

2.  40 cm

3.  20 cm 

4.  10 cm

The largest distance of the image of a real object from a convex mirror of focal length 20 cm can be:

1.   20 cm

2.  infinite

3.  10 cm

4.  depends on the position of the object.

A candle flame of 3 cm is placed at 300 cm from a wall. A concave mirror is kept at distance x from the wall in such a way that the image of the flame on the wall is 9 cm. Then x is:

1.  339 cm 

2.  900 cm

3.  450 cm 

4.  423 cm

A ray of light passes through a plane glass slab of thickness t and refractive index $\mathrm{\mu }$ = 1.5. The angle between the incident ray and emergent ray will be:

1.  0$°$

2.  30$°$

3.  45$°$

4.  60$°$

A fish looking up through the water sees the outside world contained in a circular horizon. lf the refractive index of water is 4/3 and fish is 12 cm below the surface, the radius of the circle in cm is:

1.  $12 \times 3 \times \sqrt{5}$

2.  $4 \times \sqrt{5}$

3.  $12 \times 3 \times \sqrt{7}$

4.  $12 \times 3/\sqrt{7}$

The angle of a prism is 60° and the index of refraction of glass with air is 1.5. If the angle of incidence on the first face is ${\mathrm{I}}_1$ and the angle of emergence at the second face is ${\mathrm{I}}_2$, then the prism produces minimum deviation when:

1.  ${\mathrm{I}}_1 = 0$

2.  ${\mathrm{I}}_1 > {\mathrm{I}}_2$

3.  ${\mathrm{I}}_1 < {\mathrm{I}}_2$

4.  ${\mathrm{I}}_1 = {\mathrm{I}}_2$

A lens of power +2.0 D is placed in contact with another lens of power -1.0D. The combination will behave like:

1.  a converging lens of focal length 100 cm

2.  a diverging lens of focal length 100 cm

3.  a converging lens of focal length 50 cm

4.  a diverging lens of focal length 50 cm

A biconvex lens has a focal length of 10 cm. It is cut in half and two pieces are placed as shown. The focal length(in cm) of the final combination is:

1.  10

2.  20

3.  40

4.  Not a lens

A parallel beam of light is incident on a system of two convex lenses of focal lengths ${\mathrm{f}}_1$ = 20 cm and ${\mathrm{f}}_2$ = 10 cm. What should be the distance between the two lenses so that rays after refraction from both the lenses pass undeviated?

1.  60 cm

2.  30 cm

3.  90 cm

4.  40 cm