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:

1. focal length of the lens.

2. radius of curvature of the curved surface.

3. aperture of the lens.

4. refractive index of the material.

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.