Question

Find the amplitude of electric field produced by radiation coming from a $100\,W$ bulb at a distance of $4\,m$ , assuming that the bulb is a point source and its efficiency is $3.14\%$ .

• A. $2.42\,Vm^{- 1}$
• B. $14\times 10^{4}\,Vm^{- 1}$
• C. $4.2\times 10^{4}\,Vm^{- 1}$
• D. $3.43\,Vm^{- 1}$

Answer 1

Answer: (D)

$E_{0}=\sqrt{\frac{P}{2 \pi R^{2} ϵ_{0} c}}$
$=\sqrt{\frac{3 . 14 \times 100}{2 \times 3 . 14 \times 16 \times 100 \times 8 . 85 \times 10^{- 12} \times 3 \times 10^{8}}}=3.43\,Vm^{- 1}$