81. If and K are electrical and thermal conductivity of metals, respectively at absolute temperature T. Then correct Wiedemann-Franz law in term of Lorentz number L is (1) Ko =L (2) =L T KT (3) =L (4) =L 82. The critical current which can flow through a super conductor aluminium wire of diameter 1 mm is (critical magnetic field for aluminium is 7.9 10 A/m) (1) 7.9 A (2) 15.8 A (3) 15.8 A (4) 7.9 m A 83. If kinetic energy of a particle is equal to its rest mass energy, then velocity of particle is: (1) C 3 (3) 7C2 (2) C (4) C 84. In a simple pendulum, the length of string is and mass of bob is m. Then its Lagrangian is represented at arbitrary angle 0 is (1) m/202+ mg/(1 - cos 0) (2) m/20-mgl (1-cos 0) (3) m/20+mg/ (1 + cos 0) (4) 2 mi0+mgl (1-cos 0) 85. Regarding Bessel functions, which one is correct? (1) xx(x)] = x^ Jn +1(x) (2) Jn (x)]=-x" Jn+1(x) n+1 (3) Jn (x)=J'n+1(x)+ Jn+1(x) x (4) Jn (x) Jn (-x)