38. An equiconvex lens is cut into two halves along (i) XOX and (ii) Y OY as shown in the figure. Let f, f′, f′′ be the focal lengths of the complete lens, of each half in case (i), and of each half in case (ii), respectively. Choose the correct statement from the following.

38. An equiconvex lens is cut into two halves along (i) XOX and (ii) Y OY as shown in the figure. Let f, f′, f′′ be the focal lengths of the complete lens, of each half in case (i), and of each half in case (ii), respectively. Choose the correct statement from the following.

37. A convex lens is dipped in a liquid whose refractive index is equal to the refractive index of the lens. Then its focal length will ?

Three capacitors each of capacity 4μF are to be connected in such a way that the effective capacitance is 6μF. This can be done by ?

A charge q is located at the centre of a cube. The electric flux through any face is ?

An electron is moving round the nucleus of a hydrogen atom in a circular orbit of radius r. The Coulomb force F between the two is ___ ?