Homework Help: Earth's Electric Field

1. May 27, 2004

wikidrox

I am having trouble doing this question.

Measurements indicate there is an electric field surrounding the earth. Its magnitude is about 100 N/C at the earth's surface and points to the centre of the earth. What is the magnitude of the electric charge on the earth? Is it positive or negative?
(Hint: The electric field caused by a uniformly charged sphere is the same as if the entire charge were concentrated at its centre)

2. May 27, 2004

chroot

Staff Emeritus
Look in your book and find out which direction field lines point. Do they leave positive charges and end on negative charges? Or vice versa?

- Warren

3. May 28, 2004

wikidrox

but how do I find the magnitude of the electric charge on earth?
I don't have enought information

4. May 28, 2004

chroot

Staff Emeritus
Use the definition of the field due to a point charge. Pretend that all of the earth's charge is concentrated at a point at the center of the earth. The earth's radius is 6,378.1 kilometers.

$$E = \frac{1}{4 \pi \epsilon_0} \frac{q}{r^2}$$

- Warren