The radii of curvature of the faces of a double convex lens are \(10\) cm and \(15\) cm. Its focal length is \(12\) cm. What is the refractive index of glass?
1. \(1.3\)
2. \(1.2\)
3. \(1.5\)
4. \(1.4\)

A convex lens has a \(20~\text{cm}\) focal length in air. What is the focal length in water?
(the refractive index of air-water \(=1.33,\) refractive index for air-glass \(=1.5\))
1. \(+72.72~\text{cm}\)
2. \(+78.2~\text{cm}\)
3. \(-72.72~\text{cm}\)
4. \(+70.2~\text{cm}\)

Find the position of the image formed by the lens combination in the given figure.

 

The final image is:

What focal length should the reading spectacles have for a person for whom the least distance of distinct vision is \(50~\text{cm}\)?
1. \(-50~\text{cm}\)
2. \(+50~\text{cm}\)
3. \(-60~\text{cm}\)
4. \(+60~\text{cm}\)

The far point of a myopic person is \(80~\text{cm}\) in front of the eye. What is the power of the lens required to enable him to see very distant objects clearly?
1. \(-1.25~\text{D}\) 
2. \(+1.25~\text{D}\) 
3. \(-2.12~\text{D}\) 
4. \(+2.12~\text{D}\) 

The near point of a hypermetropic person is \(75~\text{cm}\) from the eye. What is the power of the lens required to enable the person to read clearly a book held at \(25~\text{cm}\) from the eye?
1. \(+2.67~\text{D}\) 
2. \(-1.25~\text{D}\) 
3. \(-2.67~\text{D}\)
4. \(+1.25~\text{D}\)

In the diagram given below, plot of angle of deviation ($\delta$) versus angle of incidence (i) for a triangular prism is given. Then the angle of minimum deviation is-

1. ${20}^o$

2. ${30}^o$

3. ${40}^o$

4. ${50}^o$

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. \(45^{\circ}\)
2. \(90^{\circ}\)
3. \(60^{\circ}\)
4. \(30^{\circ}\)$\mathrm{}$

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

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