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Colgio Internacional de Santiago 2014/2015

Physics Worksheet A2

Unit4: Capacitors

1. A Capacitor stores a charge of 0.063 C( when it is connected to a source of emf

of 9V. What is its capacitance? How much charge will it store for an appliedpotential difference of 15 V?

2. The dome of a van de Graaff generator has a capacitance of 20 pF Calculate the

energy stored when the dome is raised to a potential of 100 kV.

3.

In an experiment to determine the electronic charge, charged oil droplets are

suspended in the electric field between two parallel plates. A droplet of mass 8.1

x .10-13 kg is held stationary between the parallel plates, of separation 1.6cm,

when a potential difference of 51 OOV is set up between the

plates. Calculate the charge on the droplet.

4. In order to ignite the air-fuel mixture in a combustion engine

there needs to be an electric field of about 10MVm-1 in the

gap in the spark plug. If the spark plug gap is 1.4 mm,

calculate the gap potential difference required to produce the

required Aspark plug field strength between the gap.

5.

A van de Graaff generator can generate a voltage of 500kV

Calculate the capacitance of the dome if it stores 7.5J of

energy when fully charged.

6.

A 68,F capacitor is charged by a potential difference of 2000V and thendischarged through a circuit with resistance 60. How long will it take to

discharge completely? What current willflow?

7.

A student sets up the charging/discharging circuit shown

opposite, to investigate the discharge of a capacitor of value

220,F. The capacitor is charged by moving the switch to

position 1 and then discharged through the large-value

resistor by moving the switch to position 2. The student reads

the discharge current every 10 s. The results table is shown.

Use a straight-line graph to determine the time constant of the

circuit, and hence calculate a value for the resistance in thecircuit.

8. A capacitor charges through a 0.22 Mresistor. Calculate the capacitance if the

time taken for it to reach full charge is 5 minutes.

9. Show that the time constantRC has units of seconds.

10. A 47,F capacitor is charged to a potential difference of 15V and then

discharged through a 100 k resistor. How long does it take for half of the

energy stored in the capacitor to have dissipated in the circuit?

o 100

10 68

20 47

30 32

40 22

50 15

60 10