Q:(1) A point charge q = +38.0 A point charge q = +38.0 mu C moves from A to B s
ID: 2276227 • Letter: Q
Question
Q:(1) A point charge q = +38.0
A point charge q = +38.0 mu C moves from A to B separated by a distance d = 0.197 m in the presence of an external electric field of magnitude 259 N/C directed toward the right as in the following figure. Find the electric force exerted on the charge. Find the work done by the electric force. Find the change in the electric potential energy of the charge. Find the potential difference between A and B. The metal sphere of a small Van de Graaff generator illustrated in the following figure has a radius of 17.9 cm. When the electric field at the surface of the sphere reaches3.0 106 V/m, the air breaks down, and the generator discharges. What is the maximum potential the sphere can have before breakdown occurs? When a 3.00-V battery is connected to the plates of a capacitor, it stores a charge of 15.0 mu C. What is the value of the capacitance? If the same capacitor is connected to a 15.00-V battery, what charge is stored?Explanation / Answer
a) F = qE = (38x10^-6) x 259 = 0.98x10^-2 N
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b) work done = force x displacement.
If A is on the left then W = 0.98x10^-2x 0.197 = 1.93x10^-3 J
If A is on the right then W = -0.98x10^-2x 0.197 = -1.93x10^-3 J
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c) The change in potential energy is simply minus whatever the answer to part b) is.
When a field, for example accelerates, a charge, the charge loses potential energy (it gets converted to kinetic energy).
(Just think of gravity. When something falls, the loss of potential energy = gain in kinetic energy; the lost potential energy is the work done by the gravitational field.)
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d) The potential difference (V) is defined as energy transferred/charge
If A is on the left V = -1.93x10^-3/(38x10^-6) = -50.78V
If A is on the right V = 1.93x10^-3/(38x10^-6) = 50.78V
The + or - signs are potentially confusing - it depends if they want the potential of A relative to B, or of B relative to A.
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