A sinusoidal electromagnetic wave has an average intensity of 100 W/m2W/m2. By what factor would the electric-field amplitude of the wave have to be increased in order for the wave to have an average intensity of 8100 W/m2W/m2

The electric field is increase to 80  so average intensity became 8100 .

Explanation:

Given :

Initial average intensity  

Final average intensity  

The average intensity is proportional to the square of the electric field.

∴  

    ∝

⇒  

So initial electric field is

Now intensity become so electric field is,

So final electric field  

So electric field increase by 80

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