# Day 111 (part 2)

1) A capacitor with air between its plates has capacitance 3.0 μF. What is its capacitance when wax of dielectric constant 2.8 is placed between the plates?

Answer (8.4 uF)

2) Determine the charge on each plate of a 0.05 μF capacitor when the potential difference between the plates is 200. V.

Answer (10 uC)

3) A capacitor is charged with 9.6 nC and has a 120 V potential difference between its terminals. Compute its capacitance and the energy store in it.

Answer (80 pF, .576 uJ)

4) Compute the energy stored in a 60. pF capacitor

(A) when it is charged to a potential difference of 2.0 kV and

(B) when the charge on each plate is 30. nC.

Answer (4.3 x 10^7 J, 7.5 uJ)

5) Three capacitors, each of capacitance 120 pF, are each charged to 500. V and then connected in series. Determine

(A) the potential difference between the end plates

(B) the charge on each capacitor and (C) the energy stored in the system.

Answer (1500 V, 60 nC, 45 uJ)

6) Three capacitors (2.0, 5.0, and 7.0 μF) are connected in series. What is their equivalent capacitance?

Answer (1.19 uF)

7) Three capacitors (2.0, 5.0, and 7.0 m F) are connected in parallel. What is their equivalent capacitance?

Answer (14 uF)

8) The capacitor combination in Problem #6 is connected in series with the combination in Problem #7. What is the capacitance of this new combination?

Answer (1.09 uF)

9) Two capacitors (0.30 and 0.50 μF) are connected in parallel. (A) What is their equivalent capacitance? A charge of 200. μC is now placed on the parallel combination. (B) What is the potential difference across it? (C) What are the charges on the capacitors?

Answer (.8 uF, 250 V, 75 uC, 125 uC) 10) A 2.0 μF capacitor is charged to 50. V and then connected in parallel (positive plate to positive plate) with a 4.0 μF capacitor charged to 100. V.

(A) What are the final charges on the capacitors?

(B) What is the potential difference across each?

Answer (167 uC, 33 uC, 83V)

11) (A) Calculate the capacitance of a capacitor consisting of two parallel plates separated by a layer of paraffin wax 0.5 cm thick, the area of each plate being 80. cm2. The dielectric constant for the wax is 2.0.

(B) If the capacitor is connected to a 100. V source, calculate the charge on the capacitor and the energy stored in the capacitor.

Answer (28 pf, 2.8 nC, 0.14 uJ)

(source)