1. Two point charges of +40.0 ?C and -10.0 ?C are separated by a distance of 20.
ID: 1276142 • Letter: 1
Question
1. Two point charges of +40.0 ?C and -10.0 ?C are separated by a distance of 20.0 cm. A +7.00 ?C charge is placed midway between these two charges. What is the electric force acting on this charge because of the other two charges? Is it towards a positive or negative charge?
2. A capacitor consists of a set of two parallel plates of area A separated by a distance d. This capacitor is connected to a battery and charged until its plates carry charges +Q and -Q. If the separation between the plates is doubled, will the electrical energy stored in the capacitor double, be cut in half, quadruple, be cut in fourth, or not change?
Explanation / Answer
(1)
q2 =7uC
q1 = 40uC
q3 = 10uC
r = 20cm
F = k q1q2 / r^2 +kq3q2 / r^2 = kq2/r^2 (q1+q3) = 78.75 N directed towards the negative charge
(2)
because energy propertional to (1/distance)
Thus the electrical energy stored in the capacitor will be cut in half
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