Problem%20Set%201%20Solutions

# Problem%20Set%201%20Solutions - 4 The fact that the spheres...

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4. The fact that the spheres are identical allows us to conclude that when two spheres are in contact, they share equal charge. Therefore, when a charged sphere ( q ) touches an uncharged one, they will (fairly quickly) each attain half that charge ( q /2). We start with spheres 1 and 2 each having charge q and experiencing a mutual repulsive force 22 / Fk qr = . When the neutral sphere 3 touches sphere 1, sphere 1’s charge decreases to q /2. Then sphere 3 (now carrying charge q /2) is brought into contact with sphere 2, a total amount of q /2 + q becomes shared equally between them. Therefore, the charge of sphere 3 is 3 q /4 in the final situation. The repulsive force between spheres 1 and 2 is finally 2 ( / 2)(3 / 4) 3 3 ' 3 0.375. 88 8 qq q F k F rr F == = = =

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18. (a) For the net force to be in the + x direction, the y components of the individual forces must cancel. The angle of the force exerted by the q 1 = 40 µ C charge on 3 20 qC = is 45°, and the angle of force exerted on q 3 by Q is at – θ where 1 2.0 cm tan 33.7 .
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## This note was uploaded on 05/04/2010 for the course PHYS 11b taught by Professor Mobius during the Spring '09 term at Harvard.

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Problem%20Set%201%20Solutions - 4 The fact that the spheres...

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