Q. No.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. \(1.4\)
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? (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.
| 1. | Final image is formed 30 cm to the right of the third lens. |
| 2. | Final image is formed 20 cm to the left of the third lens. |
| 3. | Final image is formed 30 cm to the left of the third lens. |
| 4. | Final image is formed 20 cm to the right of the third lens. |
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 \(80\) cm in front of the eye. What is the power of the lens required to enable him to see very distant objects clearly?
1. \(-1.25\) D
2. \(+1.25\) D
3. \(-2.12\) D
4. \(+2.12\) D
The near point of a hypermetropic person is \(75\) cm from the eye. What is the power of the lens required to enable the person to read clearly a book held at \(25\) cm from the eye?
1. \(+2.67\) D
2. \(-1.25\) D
3. \(-2.67\) D
4. \(+1.25\) D
If \(f=0.5\) m for a glass lens, what is the power of the lens?
1. \(+0.4\) D
2. \(+4.0\) D
3. \(+0.2\) D
4. \(+2.0\) D
A magician during a show makes a glass lens with \(n=1.47\) disappear in a trough of liquid. What is the refractive index of the liquid?
1. \( 1.47 \)
2. \( 1.33 \)
3. \(0.66 \)
4. \( 1.5\)
Light from a point source in the air falls on a convex spherical glass surface (n = 1.5 and radius of curvature = 20 cm) of a glass medium which extends till infinity on other side . The distance of the light source from the glass surface is 100 cm. At what position the image is formed?
| 1. | at a distance of 200 cm from the glass surface, in the direction of incident light. |
| 2. | at a distance of 100 cm from the glass surface, in the direction of incident light. |
| 3. | at a distance of 200 cm from the glass surface, in the opposite direction of incident light. |
| 4. | at a distance of 100 cm from the glass surface, in the opposite direction of incident light. |
The earth takes \(24~\text{h}\) to rotate once about its axis. How much time does the sun take to shift by \(1^{\circ}\) when viewed from the earth?
1. \(3~\text{minutes}\)
2. \(2~\text{minutes}\)
3. \(1~\text{minutes}\)
4. \(4~\text{minutes}\)
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