# Find the rms electric field strength of a given EM wave

• henrco
In summary, the conversation revolved around calculating the rms electric and magnetic field strengths of an electromagnetic wave with known intensity. The student had correctly calculated the answer for part 1 but was struggling with part 2. They realized that they were using the wrong value for part 2 and once they corrected it, they got the expected answer. The equation used for calculating the rms magnetic field strength was also mentioned.
henrco
Hi,

I was able to correctly calculate the answer to part 1 below but the answer to part 2 is incorrect
and I cannot see the error of my ways... any help gratefully received.

1. Homework Statement

An electromagnetic wave has an intensity of 127 W/m2.

1) Find its rms electric field strength.
2) Find its rms magnetic field strength.

Bo = Eo/c

Brms = B/sqr(2)

## The Attempt at a Solution

Answer to part 1 : Eo = 219 V/m

Part 2

Calculate Bo = 219/2.998 x 10^8 = 7.3 x 10^-7

Brms = (7.3 x 10^-7)/sqr(2) = 5.17 x 10^-7 T

Does the answer to part 1 give E0 or Erms? How do you find Brms from Erms?

henrco
Thank you for replying and your question helped me understand my mistake.

Part 1's answer was Erms, and I was using this answer for part 2 instead of using Eo.
When I recalculated using the correct value I got the answer I expected.

## 1. What is the formula for calculating the rms electric field strength of an EM wave?

The formula for calculating the rms electric field strength of an EM wave is E_rms = E_max / √2, where E_max is the maximum electric field strength of the wave.

## 2. What is the unit of measurement for rms electric field strength?

The unit of measurement for rms electric field strength is volts per meter (V/m).

## 3. How is the rms electric field strength related to the amplitude of the EM wave?

The rms electric field strength is equal to the amplitude of the EM wave divided by the square root of 2.

## 4. Can the rms electric field strength vary for different types of EM waves?

Yes, the rms electric field strength can vary for different types of EM waves depending on their frequency and amplitude.

## 5. Why is it important to calculate the rms electric field strength of an EM wave?

Calculating the rms electric field strength allows us to determine the overall strength and intensity of an EM wave, which can help us understand its potential effects on living organisms and technological devices.

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