# Homework Help: E and B-Field of 10W laser

1. May 5, 2010

### mrmonkah

1.Calculate the average E-Field and B-field produced by a laser with power 10W and radius 1mm

2.Not sure where to start with this one. Use equations of Flux perhaps?

3. So given the modest amount of infomation and the fact the question represents 1 mark, i assume the calculation is straight forward. I just dont know how to approach the question. Any help to get me started would be greatly appreciated.

2. May 5, 2010

### Dickfore

Do you know what is the physical quantity intensity and how it is related to the E and B fields of an electromagnetic wave?

3. May 5, 2010

### mrmonkah

With regards to intensity:

Power = $$\int$$ Intensity dA

|Intensity| = Power / $$\pi$$ r$$^{2}$$ : As per Area of beam.

Not sure how to relate to the Electric and Magnetic Fields.

4. May 5, 2010

### Dickfore

This just means you are able to calculate the intensity of the beam, given the data from the problem. It is an intermediate result. You need to use a specific formula that relates the intensity of an electromagnetic wave to the intensity of E and B in order to proceed further.

5. May 7, 2010

### mrmonkah

okay, i think i have the solution now,

find power density, (power/surface area),

Also Power Density = Mag of poynting Vector

That is 'Power Density = $$\frac{E^{2}}{c\mu_{0}}$$

Re-arranging for <E> for E-field.

To find B-Field, use <B> = (1/c)<E>