In: Physics
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?
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