Two identical conducting spheres carry charges of +5.0 μc and –1.0 μc, respectively. the centers of the spheres are initially separated by a distance l. the two spheres are brought together so that they are in contact. the spheres are then returned to their original separation l. what is the ratio of the magnitude of the electric force on either sphere after the spheres are touched to that before they were touched? a) 1/1 b) 4/5 c) 9/5 d) 5/1 e) 4/9

B) 4/5

Explanation:

The magnitude of the electric force between the two spheres is given by

where

k is the Coulombs' constant

q1 and q2 are the charges on the two spheres

r is the distance between the two spheres

Initially, we have

So the force is

Later, the two spheres are brought together so they are in contact: this means that the total charge will redistribute equally on the two spheres (because they are identical).

The total charge is

So each sphere will have a charge of

So, the new force will be

And so the ratio of the two forces is

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form