Constants ? Part A A capacitor consists of two 6.4-cm-diameter circular plates s

Question

Constants ? Part A A capacitor consists of two 6.4-cm-diameter circular plates separated by 1.0 mm. The plates are charged to 130 V,then the battery is removed. How much energy is stored in the capacitor? Uc-2.4 107J Ans Correct Part B After the battery is removed, the plates are pulled apart to where the distance between them is 2.0 mm. What is the final value of the potential difference between the plates? Submit Part C How much work must be done to pull the plates apart to where the distance between them is 2.0 mm? W- 2.410 J Previous Answers

Explanation / Answer

here,

diameter , d = 6.4 cm = 0.064 m

sepration between the plates , x = 1 mm = 0.001 m

potential difference , V = 130 V

a)

the energy stored , E = 0.5 * C * V^2

E = 0.5 * ( area * e0 /d) * V^2

E = 0.5 * ( pi * (0.064/2)^2 * 8.85 * 10^-12 /0.001 ) * 130^2

E = 2.41 * 10^-7 J

b)

when the battery is removed

the new potential difference , V' = V * d' /d

V' = 130 * 0.002 /0.001 = 260 V

c)

the work done , W = change in potential energy stored

W = (0.5 * area * e0 /x') * V'^2 - 0.5 * area * e0 /x ) * V^2

W = 0.5 * pi * 0.032^2 * 8.85 * 10^-12 * (260^2 /0.002 - 130^2 /0.001 ) J

W = 2.41 * 10^-7 J

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