Three pure inductors each of inductance 6H are connected as shown in the figure. Their equivalent inductance between the points 'P' and 'Q' is

A body at rest falls through a height 'h' with velocity 'V'. If it has to fall down further for its velocity to become three times, the distance travelled in that interval is

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

Photoemission from metal surface takes place for frequencies '$$v_1$$' and '$$v_2$$' of incident rays $$\left(v_1>v_2\right)$$. Maximum kinetic energy of photoelectrons emitted is in the ratio $$1: \mathrm{K}$$. The threshold frequency of metallic surface is