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DC - Parts 7 & 8 Revision

Total questions: 30

Worksheet time: 31mins

Name
Class
Date
1.

Energy is stored in a capacitor in the:

a)

magnetic field within the dielectric

b)

magnetic field around the capacitor leads

c)

electric field across the dielectric

d)

electric field across the entire circuit

2.

Capacitors store an electric charge whose magnitude depends upon the plate area, the type of dielectric and the:

a)

thickness of the plates

b)

length of the plates

c)

distance between the plates

d)

size of the plates

3.

A capacitor which has been connected to a dc supply for a period of time displays a similar electrical characteristics to that of:

a)

a closed circuit

b)

a short circuit

c)

an open circuit

d)

an a.c. circuit

4.

Increasing the value of resistance in a series RC circuit will:

a)

increase the time constant of the circuit

b)

decrease the time constant of the circuit

c)

increase the charging current

d)

minimise the voltage drop across the resistor

5.

Which of the following materials cannot be used as a dielectric?

a)

air

b)

paper

c)

carbon

d)

oil

e)

plastic

6.

The principal danger associated with charged capacitors is electric shock. This can be lethal, so capacitors should always be:

a)

allowed to cool before handling

b)

avoided at all costs

c)

discharged before handling

d)

ignored, as the shock really isn't that bad

7.

1CT=1C1+1C2+1C3\frac{1}{C_T}=\frac{1}{C_1}+\frac{1}{C_2}+\frac{1}{C_3}  For the diagram shown, the total capacitance is:

a)

230µF

b)

42.5mF

c)

23.53µF

d)

23.53F

8.

For the diagram shown, the time constant is:

a)

2.21 seconds

b)

2.21 minutes

c)

47 seconds

d)

11 seconds

9.

For the diagram shown, the time constant is 1.5 seconds.

How long will it take to fully charge the capacitor?

a)

1.5 seconds

b)

1.5 minutes

c)

7.5 seconds

d)

4.5 seconds

10.

For the diagram shown, what will be the voltage across the capacitor after one time constant?

a)

10V

b)

3.68V

c)

6.32V

d)

0V

11.

Relative Permittivity is also know as:

a)

resistivity

b)

di-electric constant (K)

c)

reluctance

d)

permissivity

12.

If the plate area and distance between the plates of a capacitor are kept constant, increasing the permittivity of the dielectric will increase the value of capacitance.

a)

True

b)

False

c)

False, permittivity is a property of inductors

13.

For the diagram shown, what will be the voltage across the resistor after one time constant?

a)

10V

b)

3.68V

c)

6.32V

d)

0V

14.

For the diagram shown, what will be the current in the circuit after one time constant?

a)

213µA

b)

78µA

c)

135µA

d)

0A

15.

From left to right, the capacitors in the images shown are:

a)

fixed, polarised, trimmer, variable

b)

fixed, polarised, variable, trimmer

c)

polarised, fixed, trimmer, variable

d)

variable, fixed, trimmer, polarised

16.

What is the SI unit for capacitance?

a)

coulomb (C)

b)

microfarad (µF)

c)

watt (W)

d)

farad (F)

17.

The image shows the capacitor voltage A and the current B curves while charging. Respectively, which curves show the capacitor voltage and the current while discharging?

a)

red curve A; green curve B

b)

green curve B; red curve A

c)

green curve B; green curve B

d)

red curve A; red curve A

18.

 Q=CVQ=CV  What is the charge on a capacitor of 470µF connected to a 400V DC supply?

a)

85C

b)

85mC

c)

188µC

d)

188mC

19.

 E=12CV2E=\frac{1}{2}CV^2  How much energy is stored in a 33µF capacitor when connected to 230V DC supply?

a)

873J

b)

873kJ

c)

873mJ

d)

873µJ

20.

 Q=CVQ=CV 
The charge on a capacitor of 220µF is 28.6mC.

What is the voltage across it?

(Hint, you need to transpose the equation)

a)

130V

b)

130kV

c)

130mV

d)

130MV

21.

Older capacitors can sometimes contain polychlorinated biphenyls (PCBs). These chemicals can cause _____________ if they come into contact with the skin.

a)

chronic fatigue

b)

cancer

c)

acid burns

d)

diabetes

e)

heart palpitations

22.

Some power capacitors in electrical equipment must be fitted with 'bleed' resistors to discharge them within _________ of removing the supply.

a)

1 minute

b)

5 minutes

c)

20 minutes

d)

30 seconds

23.

A functioning capacitor can be tested with an ohmmeter and should read:

a)

a very high resistance

b)

zero resistance

c)

a high resistance when connected to the ohmmeter and then decrease to zero

d)

a low resistance when connected to the ohmmeter and then increase to a high value

24.

Before testing capacitors with an ohmmeter, they should be fully discharged.

a)

True

b)

False

c)

Not relevant

d)

A small zap won't hurt you

25.

The image shows many types of capacitors.

Different types can be used in:

a)

voltage regulators

b)

fluorescent lights

c)

motors

d)

electronic circuits

e)

all of the above

26.

For the image shown, calculate the total capacitance.

a)

14F

b)

14µF

c)

2µF

d)

1.14F

27.

A capacitor which has been fully discharged, displays a similar electrical characteristics to that of:

a)

a closed circuit

b)

a short circuit

c)

an open circuit

d)

an a.c. circuit

28.

Work and energy are the same thing.

a)

True

b)

False

29.

What is the practical unit for capacitance?

a)

coulomb (C)

b)

microfarad (µF)

c)

watt (W)

d)

farad (F)

30.

Decreasing the value of capacitance in a series RC circuit will:

a)

increase the time constant of the circuit

b)

decrease the time constant of the circuit

c)

increase the charging current

d)

maximise the voltage drop across the resistor