Question

If the average power per unit area delivered by an electromagnetic wave is \( 9240 \, \text{Wm}^{-2} \), what is the amplitude of the magnetic field in the wave?

• A. \( 4.4 \, \mu T \)
• B. \( 6.6 \, \mu T \)
• C. \( 8.8 \, \mu T \)
• D. \( 10.2 \, \mu T \)

Hint:

Use \( S = \frac{1}{2\mu_0} c B_0^2 \) to find the magnetic field from intensity.

Answer 1

The Correct Option is C

Average power per unit area (Intensity): \( S = \frac{1}{2\mu_0} c B_0^2 \)
\[ B_0 = \sqrt{ \frac{2\mu_0 S}{c} } = \sqrt{ \frac{2 \cdot 4\pi \times 10^{-7} \cdot 9240}{3 \times 10^8} } \approx 8.8 \times 10^{-6} \, \text{T} = 8.8 \, \mu T \]