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:
                  

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 a distance \(d\) between them. If a parallel beam of light falling on \(A\) leaves \(B\) as a parallel beam, then the distance \(d\) in cm will be: 

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:

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

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. \( \frac{3}{2}\)

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. \(\frac{P}{2}\)
3. \(\frac{P}{4}\)
4. \(P\)

Two identical glass \(\left(\mu_g = \frac{3}{2}\right )\) equiconvex lenses of focal length \(f\) each are kept in contact. The space between the two lenses is filled with water \(\left(\mu_w = \frac{4}{3}\right)\). The focal length of the combination is:
1. \(\frac{f}{3}\)
2. \(f\)
3. \(\frac{4f}{3}\)
4. \(\frac{3f}{4}\)