1. Suppose you were to wrap the moon in aluminum foil and place a charge Q on it

Question

1. Suppose you were to wrap the moon in aluminum foil and place a charge Q on it. What is the capacitance of the moon in this case? (hint: it is not necassary to have two oppositely charged conductors to have a capacitor. Use the definition of potenctial for a spherical conductor and the definition of capacitance to get your answer.)

2. A parallel plate capacitor is composed of two square plates, 10.0 cm on a side, seperated byy and air gap of 0.75 mm. (a) what is the charge on this cpacitor when there is a potential difference of 150 V between the plates? (b) What energy is staored in this capacitor?

Explanation / Answer

A) capacitance of a spherical capacitor is C = 4*pi*eo*R = 4*3.142*8.85*10^-12*1737.4*1000 = 193.24 uF

2)

A) C = Q/V = eo*A/d..
A = 10*10 = 100 cm^2 = 100*10^-4 m^2

d = 0.75*10^-3 m

Q = eo*A*V/d = (8.85*10^-12*100*10^-4*150)/(0.75*10^-3) = 1.77*10^-8 C = 177 nC

B) U = 0.5*Q*V = 0.5*177*10^-9*150 = 1.32*10^-5 J

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