Find the value of the angle of emergence from the prism given below for the incidence ray shown. The refractive index of the glass is $\sqrt{3}$.

      

1. $45°$

2. $90°$

3. $60°$

4. $30°$

A lens of large focal length and large aperture is best suited as an objective of an astronomical telescope since:

1. a large aperture contributes to the quality
    and visibility of the images.

2. a large area of the objective ensures better 
    light-gathering power.

3. a large aperture provides
    a better resolution.

4. all of the above.

A point object is placed at a distance of 60 cm from a convex lens of focal length 30 cm. If a plane mirror were put perpendicular to the principal axis of the lens and at a distance of 40 cm from it, the final image would be formed at a distance of:

1. 30 cm from the plane mirror, it would be a
    virtual image.

2. 20 cm from the plane mirror, it would be a
    virtual image.

3. 20 cm from the lens, it would be a real image.

4. 30 cm from the lens, it would be a real image.

The power of a biconvex lens is 10 dioptre and the radius of curvature of each surface is 10 cm. The refractive index of the material of the lens is:
1.  $\frac{4}{3}$

2.  $\frac{9}{8}$

3.  $\frac{5}{3}$

4.  $\frac{3}{2}$

If the critical angle for total internal reflection from a medium to vacuum is $45°$, the velocity of light in the medium is: 
1. \(1.5\times10^{8}\) m/s
2. \(\frac{3}{\sqrt{2}}\times10^{8}\) m/s
3. \(\sqrt{2}\times10^{8}\) m/s
4. \(3\times10^{8}\) m/s

An object is placed on the principal axis of a concave mirror at a distance of 1.5f ( f is the focal length). The image will be at:

1.  -3f

2. 1.5f

3. -1.5f

4.  3f

A plane-convex lens of unknown material and unknown focal length is given. With the help of a spherometer, we can measure the,