NTA Abhyas JEE Main2020PhysicsUnits and DimensionsPractice
If electronic charge e , electron mass m , speed of light in vacuum c and Planck's constant h are taken as fundamental quantities, the permeability of vacuum μ 0 can be expressed in units of:
Options
- Am c 2 h e 2
- Bh m e 2
- Ch c m e 2
- Dh c e 2
Correct answer
D. h c e 2
Step-by-step solution
Magnetic potential energy inside a solenoid is U = 1 2 L I 2 Where L = self-inductor U = 1 2 μ 0 n 2 A l I 2 ∵ n = no. of turns per unit length = N l U = 1 2 μ 0 N l 2 A l I 2 U = 1 2 μ 0 N 2 l 2 A l I 2 μ 0 = 2 U l N 2 A I 2 Dimensionally, U = h c λ I = e T A = l 2 l = l ′ μ 0 = h c λ [ l ] l 2 t 2 e 2 = h λ t e 2 = h c e 2 μ 0 = h c e 2