Energy density

Aug 2017
8
0
Hi
I am confused on this question.
What I have tried so far.
Intensity=Power/area
=20 watts/π(1)^2
=1.591 W/M^2

(Erms)^2= I/(ε0*c) where ε0 is the permittivity of free space. and c is 3*10^8
The value I get for Erms is 24.4795 V/M which is wrong.
 

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