1. Practical Electricity
Intermediate 1 Physics
Practical Electricity
Questions
and
Answers
Beath High School - Int 1 Physics

2. Practical Electricity
Intermediate 1 Physics
Practical Electricity
Questions 1 to 10
Questions 11 to 20
Questions 21 to 30
Questions 31 to 40
Questions 41 to 46
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3. Beath High School - Int 1 Physics
1. Draw the circuit symbols for, a voltmeter; an electric motor; a switch and a fuse. V
voltmeter = M
electric motor =
switch =
fuse =
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2. Beside each of the following symbols write the name of the component and state what it does.
battery
supplies energy
lamp
changes electrical energy
to light energy
fixed resistor
opposes current and
produces heat
variable resistor
controls current A
ammeter
measures current
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3. Draw circuit diagrams showing:
(a) a battery, a lamp and two resistors all in series
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3. Draw circuit diagrams showing:
(b) a battery, two lamps, a switch and an ammeter all in series A
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3. Draw circuit diagrams showing:
(c) a battery and three lamps in parallel
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3. Draw circuit diagrams showing:
(d) a battery and switch in series, connected to three resistors in parallel with each other.
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4. Redraw the circuit below showing how to measure the current through the lamp. A
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5. Redraw the circuit of question 4 showing how to measure the voltage across the lamp. V
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6. Write the reading of the ammeters beside each ammeter symbol. A A
0.9 A
0.9 A A
0.9 A
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7. Redraw the circuit of question 6 without the ammeters and show how you would connect a voltmeter to measure the supply voltage V
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8. In the circuit below, the lamps are identical and the current through each lamp is 0.6 A.
Mark beside each component the value of the current through it.
0.6 A
0.6 A
1.2 A
1.2 A
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9. In the circuit below the ammeter reads 0.6 amperes.
What is the value of the current through the lamp?.
0.6 A A
0.6 A
because the current is the same everywhere in a series circuit
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10. In the circuit below, ammeter A1 reads 0.2 amperes and ammeter A2 reads 0.5 amperes.
Beside each component, write its name and the value of the current through it.
battery
0.5 A A2
lamp
0.5 A
0.5 A
resistor
0.2 A
0.2 A A1
heater
0.3 A
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11. Redraw the circuit of question 10 and show how the voltage across the lamp can be measured. A2 A1 V
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12. In this circuit, the lamps are different.
The voltmeter reads 3 volts.
What is the voltage across the other lamp L2?
8.0 V V L2
reading = Vsupply – Vlamp1
3.0 V
= 8.0 V – 3.0 V
= 5.0 V
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13. In the circuit below, the voltmeter reads 4 volts.
What is the voltage across the resistor R?
the voltage is the same across components which are in parallel. R
the voltage across R = 4 volts V
4 volts
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14. In the circuit below, the voltages are as shown.
What is the voltage of the supply?
Vsupply =
4 V + 6 V
= 10 V V V
4 V
6 V
voltages in a series circuit add up to the supply voltage.
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15. In the circuit below, the voltages are shown. What is the voltage across the second resistor?
24 V V V
8 V
Vresistor =
24 V - 8 V
= 16 V
voltages in a series circuit add up to the supply voltage.
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16. This diagram shows a 6 V bulb working correctly off a 24 V supply. What must be the voltage across the resistor?
24 V
Vresistor =
24 V - 6 V
6 V
= 18 V
voltages in a series circuit add up to the supply voltage.
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17. The diagram shows the circuit of the courtesy light in a two-door car.
A car courtesy light
operates when either door
of the car is opened.
(a) What happens to a switch when a door is opened?
(b) Explain why the switches are in parallel rather than in series.
courtesy light S1 S2
The switch closes (and completes the circuit).
This means that when either door is opened, the circuit is completed and so the courtesy lamp lights.
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18. A resistor has a voltage across it of 12 volts and a current through it of 2 amperes.
Calculate the resistance of the resistor.
voltage
current
resistance = 12 = 2 =
6 W
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19. A voltage of 6 volts is across a resistor where the current is 0.5 amperes.
What is the value of the resistor?
voltage
current
resistance = 6 =
0.5 =
12 W
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20. Calculate the resistance of a component when a voltage of 24 V causes a current of 0.1 amperes.
voltage
current
resistance = 24 =
0.1 =
240 W
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21. If a current of 2 amperes exists through a lamp when it has 12 volts across it, what is the resistance of the lamp?
voltage
current
resistance = 12 = 2 =
6 W
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22. A torch bulb is marked "6 V, 0.25 A".
Calculate the resistance of the bulb.
voltage
current
resistance = 6 =
0.25 =
24 W
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23. A resistor is placed in a circuit. The voltage across it and current through it are measured as 12 volts and 0.02 amperes.
The resistor is now removed from the circuit and an ohmmeter connected across it.
What is the reading on the ohmmeter?
voltage
current
resistance = 12 =
0.02 =
600 W
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24. (a) Find the values of the resistors in the circuit
below.
2 V
3 V
5 V V V V R1 R2 R3
0.25 A V 2 V 5
R1 = = =
8 W
R3 = = =
20 W I
0.25 I
0.25 V 3
R2 = = =
12 W I
0.25
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24. (b) Calculate the value of the supply voltage.
2 V
3 V
5 V V V V R1 R2 R3
0.25 A
voltages in a series circuit add up to the supply voltage.
so, Vsupply =
2 V + 3 V + 5 V
= 10 V
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25. Explain why it is dangerous to operate mains switches with wet hands.
The human body conducts better when wet.
It is therefore more likely that you could be electrocuted,
and mains voltage can cause a current large enough to kill you.
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26. Describe an experiment to show the change in conductivity of the human body when it is dry or wet.
Hold the terminals of an ohmmeter in separate hands.
Take a reading of the resistance of your body.
Wet your hands and repeat the experiment.
Your resistance will have reduced showing that your body is a better conductor when it is wet.
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27. Draw a sketch of a domestic three-pin plug.
Label the wires; live, neutral and earth and state the colours of their insulation.
Label the fuse and describe how it works.
e a r t h
y e l l o w
b r o w n
u s e
b l u e
cable grip
n e u t r a l
l i v e
The fuse is a wire which melts and breaks the circuit if too high a current flows.
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28. Draw the symbol for a double insulated appliance.
Describe what is meant by "double insulated".
A double insulated appliance has an insulated casing which cannot become ‘live’.
You cannot be electrocuted touching its casing and so it does not need an earth wire.
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29. What are the advantages of using a circuit breaker instead of a fuse?
A circuit breaker is faster in switching off a circuit than a fuse is
A circuit breaker is easier to reset than rewiring a fuse
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30. Which fuse value is required for an appliance with a power of 1150 watts?
current =
power
voltage
1150 =
= 5A
230
Therefore a 13 ampere fuse is required.
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31. A mains appliance has a power rating of 820 watts. How much current does it require?
current =
power
voltage
820 =
= 3.6 A
230
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32. How much current will a 2 kilowatt mains heater require?
current =
power
voltage
2000 =
= 8.7 A
230
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33. Mains plugs can have a choice of two values; 3 A and 13 A.
Which fuse should be inserted in a plug attached to a 750 watt appliance?
current =
power
voltage
750 =
= 3.3 A
230
A 3 A fuse would be too low as it would
be melted by a current of 3.3 A.
Therefore a 13 ampere fuse is required.
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34. A lighting circuit in a house serves 6 rooms. If each room can have a maximum of 150 watts per ceiling lamp, what value of fuse should be used to protect the circuit?
current =
power
voltage
6 x 150 =
230
900 =
230
= 3.9 A
Therefore a 5 ampere fuse is suitable
for this lighting circuit.
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35. Complete the following sentences to make 4 important safety rules for mains electricity.
(a) Never use worn or damaged : you could get a shock from an exposed wire.
(b) Avoid the use of if possible: too many appliances connected to an adaptor could produce at the socket.
(c) Always use the correct flex: a flex which is
too could overheat.
(d) Always use the correct plug : if the fuse rating is too and a fault develops, the flex could overheat.
flexes
live
extensions
overheating
thin
fuse
high
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36. Describe how to use a multimeter to detect an open circuit. Make sure you include how to set the multimeter to the correct setting and what you would expect to see for this fault.
Set the multimeter to be an ohmmeter (i.e. a resistance meter).
Connect the ohmmeter to the circuit.
The circuit is broken (i.e. an open circuit) if the reading is “off scale” (i.e ).
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37. The circuit shown below contains a battery, lamp, 1 A fuse and a variable resistor.
(a) Is this a series or a parallel circuit?
series
; because there is only one path for current.
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37. (b)The variable resistor is set so that a current of
2 A flows.
(i) What happens to the fuse when
there is a current of 2 A?
(ii) What happens to the lamp when
there is a current of 2 A in the
fuse? Explain your answer.
It melts/breaks/blows.
(This is because it allows a maximum current of 1 A.)
The lamp stops lighting/goes off.
This is because, when the fuse melts, the circuit is broken and so the current stops.
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38. A group of pupils investigate the time various appliances are switched on for during a day.
The appliances are all rated at 100 W.
Their results are presented in the bar chart below.
(a) Which of the appliances is switched on for the
longest time?
The lamp,
because its bar is the highest.
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38. (b) All of the appliances have a power rating of 100 W.
Explain which of the appliances is most costly to
use in one day.
The lamp,
because, being on for longer, it uses more electrical energy than the other appliances.
You should note that a higher powered appliance (like a heater) can cost more to use even if it is on for a shorter time.
This is because it is using electrical energy at a faster rate.
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39. The following table gives details about various household appliances.
(a) Complete the table shown above.
(b) List all the appliances in the table which should
have a 3 A fuse fitted in their plug.
0.26 A
8.7 A
7.8 A
1.3 A
The table lamp
and the curling tongs.
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40. Shown below is a parallel circuit containing a battery, resistor, lamp and two ammeters.
The following readings are
taken from the ammeters:
Reading on A1 = 0.05 A
Reading on A2 = 0.42 A
(a) State the current through the lamp.
(b) Which component, the resistor or the lamp, has
the larger resistance? Explain your answer. A1 A2
0.42 A
the resistor
It has a smaller current through it.
The current has split with most of it taking the easier path through the lamp.
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41. The adverts shown below give information on two music systems.
(a) Explain which music system is the more expensive to operate.
(b) Both of these systems need to be connected to the mains supply. State the voltage across these systems when connected to the mains.
(c) Calculate the current in the ‘Pony’ music system.
The VMJ one as it has a higher power rating.
230 V
current =
power
voltage 4
230 =
= A
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42. A continuity tester is shown.
(a) A piece of bare copper wire is connected to both metal probes. Will the lamp light?
Yes,
because the thick copper has a very low resistance and completes the circuit.
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42. (b) The circuit below contains 2 copper wires covered in plastic and a heater.
A test engineer suspects that there is an open circuit fault.
Describe how the continuity tester can be used to test if there is an open circuit.
Set the multimeter to be an ohmmeter (i.e. a resistance meter).
Connect the ohmmeter to the two terminals.
The circuit is an open circuit if the reading is
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42. (c) The continuity tester is connected to the L and N
pins of the plug of the appliance shown below.
The lamp does not light.
Complete the following sentences:
Since the lamp does not light this must be an circuit.
This could be because there is a wire or the on/off switch is in the position.
open
broken
off
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43. A car accessory shop sells a hand held search lamp which works with a car battery.
A motorist buys the hand held search lamp and decides to check its resistance.
(a) Complete the diagram below to show how this could
be done using an ammeter and voltmeter.
(b) How would the motorist use the readings to find
the resistance of the search lamp? (SEB 1990)
XPOWER
battery V A
resistance =
voltage reading
current reading
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44. The diagram shows the wire of a food processor
correctly connected to a three pin plug.
(a) Complete the table below naming the colour of the
insulation on the wires connected to pins L and N.
(b) One pin of the plug has not been used because the food processor is double insulated.
(i) What name is given to the pin which has not
been used?
(ii) Draw the double insulation symbol. (SEB 1990)
brown
blue
earth
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45. The circuit shown is used to investigate the effect of a variable resistor in a circuit.
The variable resistor setting is gradually changed.
The readings taken from the meters are shown in the table below.
Set 1 was the first set of readings, set 2 the second, etc.
The readings were taken in the order shown. V A
Set 1
Set 2
Set 3
Set 4
Voltage
(volts) 6
Current
(amperes)
0.1
0.2
0.3
0.4
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45. (a) Was the resistance of the variable resistor
increased or decreased during the experiment?
Explain your answer.
(b) Calculate the resistance at the lowest setting of
the variable resistor in this experiment.
Its resistance was decreased;
the current was increasing showing that it was becoming easier for current to flow.
voltage
current
resistance = 6 =
0.4 =
15 W
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46. Various appliances and the value of the fuse they need are listed below.
Computer: 3 A, Toaster: 13 A, Hair dryer: 13 A, CD player: 3 A, Coffee percolator: 3 A, Vacuum cleaner: 13 A.
Construct a table, with suitable headings, which lists the appliances in two groups. One group should contain those appliances requiring a 3 A fuse. The second group should contain those appliances requiring a 13 A fuse.
Appliances using 3 A fuse
Appliances using 13 A fuse
Computer
Toaster
CD player
Hair dryer
Coffee percolator
Vacuum cleaner
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58. Practical Electricity
Intermediate 1 Physics
Practical Electricity
End of
Questions and
Answers
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