Question

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.

• A. $1.19 × 10^{–8}\;T$
• B. $1.71 × 10^{–8}\;T$
• C. $0.84 × 10^{–8}\;T$
• D. $3.36 × 10^{–8}\;T$

Answer 1

Answer: (B)

$1.71 × 10^{–8}\;T$

Answer 2

$200 \times \frac{1}{4\pi \times 16} \times \frac{3.5}{100} = \frac{B^2_0}{2 \mu_0}C$

$μ_0 = 4π \times 10^{-7}\; T\;m/A$

$C = 3 \times 10^8\; m/sec$

⇒ $B_0 = 1.71 \times 10^{-8}\; T$