Em Waves Question 95
Question: An electromagnetic wave of frequency $ 1\times 10^{14} $ hertz is propagating along z-axis. The amplitude of electric field is $ 4V/m $ . If $ {\varepsilon _{0}}=8.8\times {{10}^{-12}}C^{2}/N-m^{2}, $ then average energy density of electric field will be:
Options:
A) $ 35.2\times {{10}^{-10}}J/m^{3} $
B) $ 35.2\times {{10}^{-11}}J/m^{3} $
C) $ 35.2\times {{10}^{-12}}J/m^{3} $
D) $ 35.2\times {{10}^{-13}}J/m^{3} $
Show Answer
Answer:
Correct Answer: C
Solution:
[c] Given: Amplitude of electric field, $ E _{0}=4,v/m $ Absolute permitivity, $ {\varepsilon _{0}}=8.8\times {{10}^{-12}}c^{2}/N-m^{2} $ Average energy density $ u _{E}=? $ Applying formula, Average energy density $ u _{E}=\frac{1}{4}{\varepsilon _{0}}E^{2} $
$ \Rightarrow u _{E}=\frac{1}{4}\times 8.8\times {{10}^{-12}}\times {{(4)}^{2}}=35.2\times {{10}^{-12}},J/m^{3} $
BETA
