Question

In: Physics

A resistor with 830? is connected to the plates of a charged capacitor with capacitance 4.60?F...

A resistor with 830? is connected to the plates of a charged capacitor with capacitance 4.60?F . Just before the connection is made, the charge on the capacitor is 7.00mC

Part A

What is the energy initially stored in the capacitor?

Part B

What is the electrical power dissipated in the resistor just after the connection is made?

Part C

What is the electrical power dissipated in the resistor at the instant when the energy stored in the capacitor has decreased to half the value calculated in part A?

Solutions

Expert Solution

Capacitance, C = 4.60 x 10^-6 F

Resistance, R = 830 ohms

Charge, Qo = 7.0 x 10^-3 C

(a)

Initial energy stored, Uo = (Qo)^2 / 2 C

= ( 7.0 x 10^-3 )^2 / ( 2 * 4.60 x 10^-6)

= 5.326 J

(b)

Current through the resistor, Io = Qo / R C

= 7.0 x 10^-3 / ( 830 * 4.6 x 10^-6 )

= 1.83 A

Power dissipated, Po = Io^2 R

                                 = (1.83)^2 * 830

                                 = 2779.59 W

(c)

U = (1/2) Uo

( Q^2 / 2 C ) = (1/2) ( Qo^2 / 2 C)

Q^2 = Qo^2 / 2

Power, P = I^2 R

                = (Q / RC)^2 R

  

                = (1/2) (Qo / RC)^2 R

                = Po / 2

                = 2779.59 / 2

                = 1389.8 W


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