physics problem

Question

A 0.11 g honeybee acquires a charge of +25pC while flying. The earth's electric field near the surface is typically (100 N/C, downward).

What electric field (strength) would allow the bee to hang suspended in the air? Express your answer to two significant figures.

My answers, 4.3 x 10^5 and 4.3 x 10^-5, are both wrong.

Answer 1

Hi Jill!

It looks like you're on the right track, and your main issue is with order of magnitude.

By setting gravitational force equal to electric force, you get

mg = qE

(mg/q) = E

Converting each quantity to SI units, we have

m = 0.11 g = 0.00011 kg

g = 9.81 m/s^2

q = 25 * 10^-12 C

Plugging these in, we get

[ (0.00011) * (9.81) / (25 * 10^-12) ] N/C = E

Running these numbers through a calculator should give you the same number, but on the order of magnitude 10^7 rather than 10^5.

Also, you may want to check whether or not they expect negative/positive signs to indicate direction of the electric field. If they do, you'll want to include that in your answer. Hope this helps!