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WorksheetsDC - Parts 7 & 8 Revision
Total questions: 30
Worksheet time: 31mins
Energy is stored in a capacitor in the:
magnetic field within the dielectric
magnetic field around the capacitor leads
electric field across the dielectric
electric field across the entire circuit
Capacitors store an electric charge whose magnitude depends upon the plate area, the type of dielectric and the:
thickness of the plates
length of the plates
distance between the plates
size of the plates
A capacitor which has been connected to a dc supply for a period of time displays a similar electrical characteristics to that of:
a closed circuit
a short circuit
an open circuit
an a.c. circuit
Increasing the value of resistance in a series RC circuit will:
increase the time constant of the circuit
decrease the time constant of the circuit
increase the charging current
minimise the voltage drop across the resistor
Which of the following materials cannot be used as a dielectric?
air
paper
carbon
oil
plastic
The principal danger associated with charged capacitors is electric shock. This can be lethal, so capacitors should always be:
allowed to cool before handling
avoided at all costs
discharged before handling
ignored, as the shock really isn't that bad
CT1=C11+C21+C31 For the diagram shown, the total capacitance is:
230µF
42.5mF
23.53µF
23.53F
For the diagram shown, the time constant is:
2.21 seconds
2.21 minutes
47 seconds
11 seconds
For the diagram shown, the time constant is 1.5 seconds.
How long will it take to fully charge the capacitor?
1.5 seconds
1.5 minutes
7.5 seconds
4.5 seconds
For the diagram shown, what will be the voltage across the capacitor after one time constant?
10V
3.68V
6.32V
0V
Relative Permittivity is also know as:
resistivity
di-electric constant (K)
reluctance
permissivity
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.
True
False
False, permittivity is a property of inductors
For the diagram shown, what will be the voltage across the resistor after one time constant?
10V
3.68V
6.32V
0V
For the diagram shown, what will be the current in the circuit after one time constant?
213µA
78µA
135µA
0A
From left to right, the capacitors in the images shown are:
fixed, polarised, trimmer, variable
fixed, polarised, variable, trimmer
polarised, fixed, trimmer, variable
variable, fixed, trimmer, polarised
What is the SI unit for capacitance?
coulomb (C)
microfarad (µF)
watt (W)
farad (F)
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?
red curve A; green curve B
green curve B; red curve A
green curve B; green curve B
red curve A; red curve A
Q=CV What is the charge on a capacitor of 470µF connected to a 400V DC supply?
85C
85mC
188µC
188mC
E=21CV2 How much energy is stored in a 33µF capacitor when connected to 230V DC supply?
873J
873kJ
873mJ
873µJ
Q=CV
The charge on a capacitor of 220µF is 28.6mC.
What is the voltage across it?
(Hint, you need to transpose the equation)130V
130kV
130mV
130MV
Older capacitors can sometimes contain polychlorinated biphenyls (PCBs). These chemicals can cause _____________ if they come into contact with the skin.
chronic fatigue
cancer
acid burns
diabetes
heart palpitations
Some power capacitors in electrical equipment must be fitted with 'bleed' resistors to discharge them within _________ of removing the supply.
1 minute
5 minutes
20 minutes
30 seconds
A functioning capacitor can be tested with an ohmmeter and should read:
a very high resistance
zero resistance
a high resistance when connected to the ohmmeter and then decrease to zero
a low resistance when connected to the ohmmeter and then increase to a high value
Before testing capacitors with an ohmmeter, they should be fully discharged.
True
False
Not relevant
A small zap won't hurt you
The image shows many types of capacitors.
Different types can be used in:
voltage regulators
fluorescent lights
motors
electronic circuits
all of the above
For the image shown, calculate the total capacitance.
14F
14µF
2µF
1.14F
A capacitor which has been fully discharged, displays a similar electrical characteristics to that of:
a closed circuit
a short circuit
an open circuit
an a.c. circuit
Work and energy are the same thing.
True
False
What is the practical unit for capacitance?
coulomb (C)
microfarad (µF)
watt (W)
farad (F)
Decreasing the value of capacitance in a series RC circuit will:
increase the time constant of the circuit
decrease the time constant of the circuit
increase the charging current
maximise the voltage drop across the resistor
