1) A capacitor consists of two 6.0-cm-diameter circular plates separated by 1.0

Question

1) A capacitor consists of two 6.0-cm-diameter circular plates separated by 1.0 mm. The plates are charged to 170V , then the battery is removed.

A) How much energy is stored in the capacitor?

B) How much work must be done to pull the plates apart to where the distance between them is 2.0 mm?

2) The highest magnetic fields in the world are generated when large arrays, or "banks," of capacitors are discharged through the copper coils of an electromagnet. At the National High Magnetic Field Laboratory, the total capacitance of the capacitor bank is 32 mF. These capacitors can be charged to 16 kV.

A) What is the energy stored in the capacitor bank when it is fully charged?

B) When discharged, the entire energy from this bank flows through the magnet coil in 10 ms. What is the average power delivered to the coils during this time?

Explanation / Answer

1. eenrgy U    = 0.5 CV^2

C   = eoA/d

C = 8.85 e-12 * 3.14* 0.03 *0.03/1e-3)

C = 25 pF

so
eenrgy U = 0.5 * 25 e-12 * 170*170

U = 3.612 *10^-7 Joules

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work DOne W = 0.5 CV^2

C now = C   = eoA/d

C = 8.85 e-12 * 3.14* 0.03 *0.03/2e-3)

C = 12.5 pF

so Work Done W = 0.5 * 12.5 e-12 * 170*170

W = 1.806 *10^-7 Joules

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energy U = 0.5 CV^2

U = 0.5 * 0.032 * 16000*16000

U = 4.1 MJ

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Power = emenry/time

P = 41. e6/10 e-3

P = 4.1 *10^9 Watt

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