1. Capacitors C 1 = 3450 nF and C 2 = 700 nF are initially connected in parallel

Question

1. Capacitors C1 = 3450 nF and C2 = 700 nF are initially connected in parallel and hold a combined charge of Qtoti = 783 nC. Find the charge on each capacitor Q1i , Q2i and the total energy Utoti stored in the system. The capacitors are then disconnected and reconnected, still in parallel, but with the terminals of one capacitor reversed, so that the positively charged side of C1 is now connected to the negatively charged side of C2 and vice versa. Find the combined charge Qtotf and total energy stored in the final state. (Remember, the total charge one the entire capacitor is zero, but Q is the magnitude of the charge on one side.)

2. A coaxial cable consists of a cylindrical metal sheath of radius b = 3.5 cm surrounding a conducting wire with outer radius a = 0.6 cm. Find the capacitance per unit length of the cable.

Explanation / Answer

As the two capacitors are connected in parallel the voltage across them is same

Q1/C1 = Q2/C2

and Q1+Q2 = 783nc

Q1/Q2 = C1/C2

= 3450/700

=4.93

Q1 = 4.93 * Q2

substituting this in the above equation gives

Q2 = 132.04 nC

Q1 = 650.95 nC

Total energy stored = 1/2 Q1C1 + 1/2 Q2C2

= 1/2 * 650.95*3450 + 1/2 * 132.04 * 700

= 1.17 * 10^-12 joules

Related Questions

Navigate

• Browse (All)
• Browse 1
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.