Three identical metal spheres on insulating stands, like in question 1, are used

Question

Three identical metal spheres on insulating stands, like in question 1, are used in an experiment. Initially sphere 1 is charged and 2 and 3 are neutral, but then a student touches sphere 1 to sphere 2 and then touches sphere 2 to sphere 3. She then places spheres 1 and 2 on a lab table so that their centers are 20 cm apart and moves sphere 3 to another part of the lab. She determines that the electrostatic force that acts between spheres 1 and 2 is 0.04 N. If the initial charge on sphere 1 is +Q a) Describe the charge state (in terms of Q) of each sphere after the described procedure has been completed. Is the measured force repulsive or attractive? Explain your reasoning. b) Determine Q.

Explanation / Answer

If initial charge of sphere1 is Q .. then

after touching sphere 1 & 2 ,, their charges will become Q/2

after touching 2 & 3 , charge of each will become Q/4

so.. the final charge are :

a)

sphere1 = Q/2

sphere 2 = Q/4

sphere 3 = Q/4

The force will be repulsive as all the charges are +ve..

b) so.. force between 1 & 2 = K * (Q/2)*(Q/4) / ( 0.2^2 ) = 0.04

so.. 9 * 10^9 * Q^2 / ( 8 * 0.04 ) = 0.04

so.. Q = 1.19257 * 10^-6 C

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