JEE Main202224 Jun 2022Evening ShiftPhysicsElectromagnetic WavesActual
An electric bulb is rated as 200 W . What will be the peak magnetic field at 4 m distance produced by the radiations coming from this bulb? Consider this bulb as a point source with 3 . 5 % efficiency.
Options
- A1 . 19 × 10 - 8 T
- B1 . 71 × 10 - 8 T
- C0 . 84 × 10 - 8 T
- D3 . 36 × 10 - 8 T
Correct answer
B. 1 . 71 × 10 - 8 T
Step-by-step solution
Intensity of light is I = Power Area = 200 × 3 . 5 100 4 π 4 2 = 0 . 034   W   m - 2 Using the relation between magnetic field and intensity, I = B 0 2 c 2 μ 0 We have, magnetic field as B 0 = I × 2 μ 0 c = 0 . 034 × 2 × 4 π × 10 - 7 3 × 10 8 = 1 . 69 × 10 - 8   T ≈ 1 . 71 × 10 - 8   T