1. | infinity | 2. | \(+2~\text{D}\) |
3. | \(+20 ~\text{D}\) | 4. | \(+5~\text{D}\) |
A concave lens of focal length \(-25\) cm is sandwiched between two convex lenses, each of focal length, \(40\) cm. The power in dioptre of the combined lens would be:
1. | \(55\) | 2. | \(9\) |
3. | \(1\) | 4. | \(0.01\) |
A convex lens A of focal length \(20~\text{cm}\) and a concave lens \(B\) of focal length \(5~\text{cm}\) are kept along the same axis with the distance \(d\) between them. If a parallel beam of light falling on \(A\) leaves \(B\) as a parallel beam, then distance \(d\) in \(\text{cm}\) will be:
1. \(25\)
2. \(15\)
3. \(30\)
4. \(50\)
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:
1. | \(30~\text{cm}\) from the plane mirror, it would be a virtual image. |
2. | \(20~\text{cm}\) from the plane mirror, it would be a virtual image. |
3. | \(20~\text{cm}\) from the lens, it would be a real image. |
4. | \(30~\text{cm}\) from the lens, it would be a real image. |
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. |
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. | \( \dfrac{4}{3} \) | 2. | \( \dfrac{9}{8} \) |
3. | \( \dfrac{5}{3} \) | 4. | \( \dfrac{3}{2}\) |
A biconvex lens has power \(P.\) It is cut into two symmetrical halves by a plane containing the principal axis. The power of one part will be:
1. | \(0\) | 2. | \(\dfrac{P}{2}\) |
3. | \(\dfrac{P}{4}\) | 4. | \(P\) |