Q49. If two cylinders (one hollow and other solid) of same length, mass and material are given, then, to twist the cylinders through the same angle: (a) More torque is needed for the hollow cylinder than the solid one (b) Couple per unit twist for solid cylinder will be more than the hollow one (c) Couple per unit twist for solid as well as hollow cylinders will be the same (d) More torque is needed for the solid cylinder than the hollow one Q54. For a two dimensional free electron gas, the electron density n and Fermi energy are related as: (a) n = m EF 2h (b) n = me h- (c) n = (2m )/2 3 (d) n = 3/2 (2m ) / EF