capacitors are often used to measure small motions. Suppose you have a parallel
ID: 582199 • Letter: C
Question
capacitors are often used to measure small motions. Suppose you have a parallel plate capacitor which is connected a 3v power supply. The pates are squares 2.5mm on a side and the separation between them is 1mm. a)What is the capacitance of this capacitor? b)How much charge is on the capacitor when it is connected to the power supply? c)now suppose one of the plates is pushed and moves .2mm closer to the other. What is the new capacitance of the capacitor? If the voltage stays the same, what is the new charge on the capacitor? d) if this motion of .2mm takes place of .03 seconds, what is the current that flows into the capacitor because of the change in plate separation?
Explanation / Answer
a)
Capacitance is C = e0*A/d
C = 8.85*10^-12*2.5^2*10^-6/10^-3
C = 44.8 * 10^-15 F
b)
Q =CV
Q = 44.8 * 10^-15 * 3
Q = 134.4 *10^-15 Couloumbs
c)
New capacitance is
Capacitance is C = e0*A/d
C = 8.85*10^-12*2.5^2*10^-6/0.8*10^-3
C =56* 10^-15 F
d)
i = q/t = (56-44.8)*3*10^-15/ 0.03 = 1.12*10^-12 A
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