Optics Question 179
Question: A lamp emits monochromatic green light uniformly in all directions. The lamp is 3% efficient in converting electrical power to electromagnetic waves and consumes 100W of power. The amplitude of the electric field associated with the electromagnetic radiation at a distance of 10m from the lamp will be
Options:
A) 1.34 V/m
B) 2.68 V/m
C) 5.36 V/m
D) 9.37 V/m
Show Answer
Answer:
Correct Answer: A
Solution:
$ S _{av}=\frac{1}{2}{\varepsilon _{0}}cE _{0}^{2}=\frac{P}{4\pi R^{2}} $
Therefore $ E _{0}=\sqrt{\frac{P}{2\pi R^{2}{\varepsilon _{0}}C}} $
$ =\sqrt{\frac{3}{2\times 3.14\times 100\times 8.85\times {{10}^{-12}}\times 3\times 10^{8}}} $ = 1.34 V/m
