SP212/3321&5521
Chapter 25 - Worksheet #2
Question 1: (a) You have a capacitor (of initial capacitance C0 ) attached to a battery and fully
charged. The capacitor stores 10 J of energy in its electric field. You then pull the capacitors plates
apart to double their separation, thereby decreasing the capacitance to C0 /2. How much energy is
stored in the capacitor now? (b) You have a capacitor (of initial capacitance C0 )that has been fully
charged, but is then separated from the battery or any circuit. The capacitor stores 10 J of energy
in its electric field. You then pull the capacitors plates apart to double their separation, thereby
decreasing the capacitance to C0 /2. How much energy is stored in the capacitor now?
Question 2: A parallel plate capacitor consists of two circular plates, each with radius R=0.0085 m,
separated by a distance of d=0.0025 m. How much potential energy is stored in this capacitor if a
potential difference of 15 V is applied across it?
Question 3: An air-filled parallel plate capacitor features square metal plates, 0.025 m long on each
side, separated by a distance of 0.0035 m. The largest magnitude electric field that can exist between
these plates before electric breakdown of the air occurs is 3.00×106 N/C. (a) What is the largest
energy density that can be held in the electric field of this capacitor? (b) What is the largest amount
of energy that can be stored in this capacitor?
SP212/3321&5521
Chapter 25 - Worksheet #2
Question 4: A 3.0 µF capacitor and a 6.0 µF capacitor are connected in series to a 9.0 V battery.
(a) What is the equivalent capacitance of the two, and how much total energy is stored by the
capacitors (i.e. how much energy is stored by the equivalent capacitor)? (b) How much energy is
stored in the 3.0 µF capacitor? (c) How much energy is stored in the 6.0 µF capacitor?
3.0 µF
9.0 V
6.0 µF
Question 5: A 3.0 µF capacitor and a 6.0 µF capacitor are connected in parallel to a 9.0 V battery.
(a) What is the equivalent capacitance of the two, and how much total energy is stored by the
capacitors (i.e. how much energy is stored by the equivalent capacitor)? (b) How much energy is
stored in the 3.0 µF capacitor? (c) How much energy is stored in the 6.0 µF capacitor?
9.0 V
3.0 µF
6.0 µF