KIRKCALDY HIGH SCHOOL
Physics Department
Physics
Electricity and Energy
3.2 Electricity
Circuit Symbols
In the questions below, fill in the correct circuit symbol for each device.
4.
Crossing
Measure
3.
Joining
Voltmeter
Energy supplies
2.
Wire
Cell
Resistors
wires
1.
Resistor
Variable Resistor
LDR
Thermistor
Lamp (bulb)
Switch
Fuse
Capacitor
Microphone
Loudspeaker
Motor
Diode
Other Components
5.
Ammeter
Ohmmeter
Oscilloscope
Battery
DC power supply
AC power supply
Photovoltaic Cell
L.E.D.
Series Circuits
Circuits, Symbols and Meters
Circuits,
Symbols
and Meters
6. a) In
the circuit
below, name the components labelled A, B, C, D
6. a) In the circuit below, name the components labelled A, B, C, D and E.
6.
a) and
In the
circuit
below,
name the components labelled A, B, C, D and E.
E.
A
B
E A A
Circuits, Symbols and Meters
A
B
E
6. a) In the circuit below, name the components labelled A, B, C, D and E.
D
C
D
C
A
A or
B
b) Stateb)whether
this iswhether
aEseries
parallel
circuit. or parallel
State
this
a series
circuit.
b) State whether
this is a series
orisparallel
circuit.
7.
Look at the circuit below.
7.
at at
thethe
circuit
below.below.
7. Look
Look
circuit
D
C
b) State whether this is a series or parallel circuit.
7.
8.
Look at the circuit below.
V
V
a) Write down the names of the components
that are connected in series.
V components that are connected in series.
a) Write down the names of the
b) Write
downWrite
the names
of the
components
that components
are connected that
in parallel.
the
of the
are
b) a)
Write down
thedown
names
of names
the components
that are connected in
parallel.
connected in series.
In the circuits
below,
identify
the meters
1,of2, the
3, 4, 5 and 6.
b) circuits
Write
down
the
names
8.
In the
below,
identify
the meters
1, 2,components
3, 4, 5 and 6. that are
a) Write down the names of the components that are connected in series.
connected
b) Write down
the namesinofparallel
the components that are connected in parallel.
8.8. In
In the
the circuits
below,
identify
the meters
2, 3, 4, 5 1,
and
circuits
below,
identify
the1,meters
2,6.3, 4, 5 and 6.
2
1
4
2
3
1
9.
5
3
2
1
5
4
4
5
6
6
3
downdown
the rule
at allatpoints
in a series
circuit.
9.a) Write
a) Write
the for
rulethe
forcurrent
the current
all points
in a series
circuit.
6
b) Write
down
the
relationship
between
the
supply
voltage
and
the
b) Write down the relationship between the supply voltage andpotential
the potential
differences
(voltages)
across
the individual
components
in a series
circuit.
differences
(voltages)
across
the individual
components
in a series
circuit.
9.
a) Write down the rule for the current at all points in a series circuit.
b) Write
down
relationship
between
thethe
supply
voltage
and
potential
9 Write
a)down
Write
down the
rule for
current
at
allthe
points
in ainseries
10. 10.
a)
thethe
relationship
between
the
supply
current
and
the
thein the
a) differences
Write down
the relationship
between
the
supply
current
andcurrents
the currents
(voltages)
across
the
individual
components
in
a
series
circuit.
branches ofcircuit.
a parallel circuit.
branches of a parallel circuit.
b) Write
downdown
the potential
difference
(voltage)between
rule for
components
that are
b)
Write
down
the difference
relationship
the
supply voltage
b) Write
Write
potential
ruleallfor
thatand
are
10. a)
down thethe
relationship
between the(voltage)
supply current
andall
thecomponents
currents in the
connected
in
parallel.
the
potential
differences
(voltages)
across
the
individual
connected in parallel.
branches of a parallel circuit.
b) Write down
the potentialindifference
components
a series(voltage)
circuit.rule for all components that are
connected in parallel.
GMV
Physics:
Electricity and Electronics (Int 2) – Student Material
Physics: Electricity and Electronics (Int 2) – Student Material
Physics: Electricity and Electronics (Int 2) – Student Material
34 34
34
Series Circuits
10
a)
b)
11.
a)
b)
11.
a)
b)
A
B
C
D
E
F
12.
Write down the relationship between the supply current and
the currents in the branches of a parallel circuit.
Write down the potential difference (voltage) rule for all
components that are connected in parallel.
Which of the following statements is/are true for series
circuits.
Which of the following statements is/are true for parallel
circuits.
A There is only one pathway round the circuit.
B There is more than one pathway around the circuit.
Which of the
following
statements
is/are truearound
for series
C The
potential
differences
thecircuits.
circuit add up to
Which of the following
statements
is/are
true
for
parallel
circuits.
the supply voltage.
D The potential difference (voltage) is the same across
There is only one pathway round the circuit.
all components.
There is more than one pathway around the circuit.
E The
current
is the
allup
points
the circuit.
The potential
differences
around
thesame
circuitatadd
to thein
supply
voltage.
F The
current
through
each
adds up to the
The potential
difference
(voltage)
is the
samecomponent
across all components.
The current issupply
the same
at all points in the circuit.
current.
The current through each component adds up to the supply current.
12.
In the circuit below the ammeter reading is 0.5 A and the
In the circuit below the ammeter reading is 0.5 A and the voltmeter reading is 4 V.
voltmeter reading is 4 V.
+
-
12 V
0.5 A
A
V
4V
13.
a)
State whether this is a series circuit or a parallel circuit.
a) State whether this is a series circuit or a parallel circuit.
b) is the current
i) through
What
the current through the lamp?
b) i) What
theislamp?
ii) difference
What isacross
the potential
ii) What is the potential
the lamp? difference across the
lamp?
In the circuit below the ammeter reads 0.8 A, the current through the lamp is 0.3 A and
the voltmeter reads 6 V.
+
6V
0.8 A
X
A
0.3 A
Y
V
GMV
a) Is this a series or a parallel circuit?
6V
4V
a) State whether this is a series circuit or a parallel circuit.
b) i) What is the
current
through the lamp?
Series
Circuits
ii) What is the potential difference across the lamp?
the circuit
below
the
ammeter
reads
0.8 A,
theAcurrent
through
In the circuit below13.
the In
ammeter
reads 0.8
A, the
current
through
the lamp
is 0.3
and
the voltmeter reads 6 V.the lamp is 0.3 A and the voltmeter reads 6 V.
+
6V
0.8 A
X
A
0.3 A
Y
V
6V
a) Is this a series or a parallel circuit?
b) i) What are the current
X and at
a) Isvalues
this aatseries
orY?
a parallel circuit?
ii) What is the potential difference across the lamp?
b)
i) What are the current values at X and at Y?
ii) What is the potential difference across the lamp?
14. Find the missing currents and voltages in the following circuits.
ysics: Electricity and Electronics (Int 2) – Student Material
35
NUMERICAL ANSWERS
Circuits
2. a) 240 C
b) 7.3 A
3. a) 144 000 C b) 72 000 s or 20 hours
c) constant current
4. b) i) metals ii) pencil ‘lead’ is carbon
11. a) A, C, E
b) B, D, F
12. a) series
b) 0.5 A
c) 8 V
13. a) parallel
b) i) X: 0.8 A, Y: 0.5 A
c) 6 V
14. a) I1 = 0.4 A b) V1 = 9 V, I2 = 1.5 A
c) I3 = 0.8 A, I4 = 0.8 A, V2 = 9 V
d) I5 = 1.5 A, I6 = 1 A, V3 = 4 V
15. 70 mV, 650 mV, 980 mV, 2963 mV, 3200 mV
16. 0.002 A, 0.029 A, 0.03 A, 5.805 A, 8.9 A, 120 A
17. a) current
b) 1.2 A, 0.6 A, 240 mA, 2.4 mA down the table
18. 6 W
19. 50 W
20. 0.009 A
21. 0.01 A
22. a) R = 75 W b) I = 1.8´10-4 A
c) V = 75 V d) R = 100 W
23. a) 18 V
b) 300 W
24. a) Table 1: 10, 10.3, 10.6, 12 down the table
GMV
Table 2: 10 for all entries down the table
25. a) 16 W
b) 2 kW
c) 1.6 kW
26. a) 2 W
b) 3 W
c) 9 W
d) 4 W
e) 3.6 W
f) 6.8 W
Series Circuits
Helpful Hint
The rules for series circuits are:
1.
2.
1.
the current is the same at all points in the circuit
the voltage of the source is shared amongst the
components in the circuit.
Two identical 2·5 V bulbs are connected to a supply as shown. What is
the voltage of the supply?
2·5 V
2·5 V
2. Four identical resistors are connected across a 12 V supply as shown
in the diagram. What is the voltage across each of the resistors?
12 V
A
3.
B
C
D
A simple circuit with a bulb and resistor in series is shown below.
36 V
12 V, 36 W
(a)
(b)
GMV
R
If the bulb is operating at its correct voltage and power
rating what is the voltage across the resistor R?
The current in the bulb is 3 A. What current flows in the
resistor?
Series Circuits
4.
Two resistors are connected in series to a supply as shown in the
diagram.
15 V
200 
(a)
(b)
5.
100 
The current in the 200  resistor is 0·05 A. What is the
current in the other resistor?
The voltage across the 100  resistor is 5 V. What is the
voltage across the 200  resistor?
A rheostat is used as a dimmer switch in a simple series circuit as
shown.
14 V
The rheostat is adjusted until the bulb is shining brightly. The
voltage across the bulb is 13·8 V and the current through the
rheostat at this setting is 1·7 A.
(a)
(b)
Calculate the voltage across the rheostat.
What is the current flowing in the bulb?
Section 4 - Useful Circuits
Series Circuits(p18)
1. 5 V
2. 3 V
3.
(a) 24 V
(b) 3 A
4.
(a) 005 A
(b) 10 V
5.
(a) 02 V
(b) 17 A
GMV
Electrical Measurements
GMV
Parallel Circuits
Helpful Hint
The rules for parallel circuits are:
1.
the voltage is the same across all the components in
parallel.
the current from the supply is shared amongst the
different branches of the circuit.
2.
1.
Two resistors are connected in parallel to a 12 V battery.
(a)
(b)
(c)
What is the voltage across R1?
What is the voltage across R2?
What size of current is drawn
from the battery?
12 V
0·3 A
R1
R2
2.
6V
Two identical bulbs and a resistor are
connected in parallel to a 6 V supply.
4A
L1
(a)
(b)
L2
R1
What is the voltage across L2 ?
A current of 1·8 A flows through
each of the bulbs.
What is the current flowing through
the resistor?
3. An electric fire has three elements which can be switched on and off
independently. The elements are connected in parallel to the mains
supply. Each element draws a current of 0·3 A when switched on.
230 V
a)
(b)
(c)
GMV
What is the voltage across the middle
element?
What is the total current flowing
from the supply when two of the
elements re switched on?
What is the maximum current drawn from
the mains by the fire?
Parallel Circuits
4.
The headlamps and side lights in a car are connected in parallel. The diagram
below shows how they are connected. The side lights (L1 & L2) may be
switched on by themselves using switch S1. The headlights (H1 & H2) are
switched on by switch S2 and only come on if the sidelights are already on.
S2
S1
12 V
(a)
(b)
(c)
(d)
5.
L2
L1
H2
H1
What is the voltage across the sidelight L1?
What is the voltage across the headlight H2?
Each sidelight draws a current of 3 A from the car battery.
What is the total current drawn from the battery when S1
only is closed?
Each headlight draws a current of 5 A from the car battery.
What is the total current drawn from the battery when S1
and S2 are closed?
A hairdryer contains a motor and heating elements (resistors). The
hairdryer shown below has three heat settings- cold, warm and hot.
The circuit diagram shows how these settings are achieved using
switches A, B and C
A
230 V
B
M
C
H1
H2
The motor draws a current of 3 A from the mains and the heating
elements draw a current of 2 A each from the mains.
(a)
Which switches must be closed to make the hairdryer blow
warm air?
(b)
What current is drawn from the mains when the hairdryer
blows warm air?
(c)
Which switches must be closed to make the hairdryer blow
hot air?
(d)
What current is drawn from the mains when the hairdryer blows
hot air?
(e)
What is the minimum current drawn from the mains when the
hairdryer is on?
(f)
What is the voltage across the motor?
GMV
Parallel Circuits
Parallel Circuits
1.
(a) 12 V
(b) 12 V
(c) 05 A
2.
(a) 6 V
(b) 04 A
3.
(a) 230 V
(b) 06 A
(c) 09 A
4.
(a) 12 V
(b) 12 V
(c) 6 A
(d) 16 A
5.
(a) A & B
(b) 5 A
(c) A, B & C
(d) 7 A
(e) 3 A
(f) 230 V
GMV
(p.20)
Voltage, Current and Resistance
In this section you can use the equation:
voltage = current x resistance
also written as:
V = IR
where
V = voltage in volts (V)
I = current in amps (A)
R = resistance in ohms ().
Helpful Hint.
Many appliances run from mains voltage which is 230 V ac.
Useful units for electricity are:
1 A = 0·000 001 A = 1 x 10-6 A
1 mA = 0·001 A = 1 x 10-3 A
1.
Find the missing values in the following table.
Voltage (V)
(a)
(b)
(c)
(d)
(e)
(f)
2.
(a)
230
24
120
6
Current (A)
Resistance ()
15
0·2
35
1 000
125
550
12
6·25 x 10-3
Look at the following circuits and calculate the supply voltage in
each case:
(b)
Vs
Vs
GMV
Vs
2·56
A
10 A
5
(c)
250 
50 mA
480 
Voltage, Current and Resistance
3.
(a)
Look at the following circuits and calculate the current in each
case:
24 V
(b)
12 V
(c)
48 V
I
I
12 
I
50 
550 
4. Look at the following circuits and calculate the unknown resistance in
each case:
(a)
24 V
(b)
12 V
25
mA
R
(c)
48 V
30 A
R
660 A
R
5. Calculate the resistance of a lamp if the current through it is 10 mA
when operated by a 24 V supply.
6. A power drill is operated at mains voltage and has a resistance of
1·5 k. Calculate the current through the drill.
7. The maximum current an electric motor can safely handle is 10 mA
and it has a resistance of 360 . Calculate its safe operating voltage.
8. A cooker draws a maximum current of 28·75 A and has a resistance
of 8 . At what voltage should it operate?
9. Hairdryers work from the mains voltage and can have currents of up
to 15 mA flowing through them. Calculate the resistance of the
hairdryer.
10. Overhead cables have resistance of 25 k. If the voltage across the
cables is 4000 V calculate the current through them.
Section 3 - Resistance
Voltage, Current & Resistance(p.6)
1.
GMV
Voltage, Current and Resistance
(a) 525 V
(b) 200 V
(c) 184 A
(d) 004 A
(e) 10 
(f) 960 
2.
(a) 50 V
(b) 640 V
(c) 24 V
3.
(a) 2 A
(b) 024 A
(c) 009 A
4.
(a) 960 
(b) 400 000 
(c) 72 727 
5. 2 400 
6. 015 A
7. 36 V
8. 230 V
9. 15 333 
10. 016 A
GMV
Electrical Resistance
1.
Rewrite the following list of potential differences (voltages) in
millivolts and arrange in order of increasing value.
0.65 V, 980 mV, 0.07 V, 3.2 V, 2963 mV
2.
Rewrite the following list of currents in amperes and then arrange in
order of increasing value.
5805 mA, 2 mA,
29 mA, 120 A,
8.9 A,
0.03 A
3.
In a series circuit, the ammeter reading was noted for different
values of resistor in the circuit.
a) Which electrical quantity does the ammeter measure?
b) Copy and complete the table below, placing the ammeter
readings in the correct order.
0.6 A, 2.4 mA, 1.2 A, 240 mA.
Resistor (Ω)
5
10
20
2.5k
Current ( )
4.
The current in a lamp bulb was 2 A when connected to a 12 V
battery. Calculate the resistance of the lamp bulb.
5.
When connected across a 3 V supply, the current in a resistor was
60 mA. What is the value of the resistor?
6.
7.
Int 2
A 220
resistor is connected across a 2 V supply. What is the
current in the resistor?
A 12 V transformer is connected to a circuit of resistance 1.2 kΩ.
What is the current in the circuit?
21.
A 12 V transformer is connected to a circuit of resistance 1.2 kW. What is the current in
the
21.circuit?
A 12
V transformer is connected to a circuit of resistance 1.2 kW. What is the current in
Electrical
Resistance
the circuit?
22. Calculate the missing quantities in the circuits below.
8. 22.
Calculate
thethemissing
the
circuits
below.
Calculate
missingquantities
quantities ininthe
circuits
below.
a)
b)
+
+
a)
b)
1.5 V +
4.5 V +
0.02 A
1.5 V
I=?
4.5 V
0.02 A
I=?
25 k W
R=?
+
-
V=?
c)
R=?
+
-
V=?
c)
+
6V
d)
15 mA
25 k W
+
60 mA
6V
d)
15 mA
60 mA
5 kW
R=?
5 kW
R=?
diagram
a 6mA
V 60
mA
lamp working
off
a 24 V
23.9. TheThe
diagram
belowbelow
showsshows
a 6 V 60
lamp
working
off a 24 V
supply.
supply.
23.
The diagram below shows a 6 V 60 mA lamp working off a 24 V supply.
+
24 V +
24 V
R
6 V 60 mA
R
6 V 60 mA
a) What must be the potential difference across the resistor if the lamp is operating
What must be the potential difference across the resistor if the lamp is
correctly?
a) What must be the potential difference across the resistor if the lamp is operating
operating
correctly?
the value
of theR.resistance of resistor R.
b) Calculate
the valueCalculate
of the resistance
of resistor
correctly?
b) Calculate the value of the resistance of resistor R.
24.
Potential difference and current were measured in both circuits below for different
values
currentdifference and current were measured in both circuits below for different
24. of
Potential
values of current
A
A
A
A
V
V
V
V
The results for each circuit are shown over the page.
The results for each circuit are shown over the page.
Physics: Electricity and Electronics (Int 2) – Student Material
Physics: Electricity and Electronics (Int 2) – Student Material
Int 2
37
37
a) What must be the potential difference across the resistor if the lamp is operating
correctly?
b) Calculate the value of the resistance of resistor R.
Electrical Resistance
24.
Potential difference and current were measured in both circuits below for different
10.values
Potential
difference and current were measured in both circuits
of current
below for different values of current
A
A
V
V
The results for each circuit are shown over the page.
The results for each circuit are shown over the page.
V (V)
I (A)
V/I (ohms)
V (V)
2.4
0.24
2.4
3.1
0.30
3.0
0.34
Physics:3.6
Electricity and
Electronics (Int 2) – Student Material 3.4
4.8
0.40
4.0
a)
b)
c)
d)
e)
11.
I (A)
0.24
0.30
0.34
0.40
V/I (ohms)
Copy and complete both tables.
What is the purpose of the variable resistor in the above circuits?
What conclusion can be drawn about the resistance of the lamp bulb
as the current increases?
What conclusion can be drawn about the resistance of the resistor
as the current increases?
Explain the difference in the behaviour of the lamp bulb and the
resistor as the current increases.
Calculate the total resistance between X and Y for the following.
12. Calculate the total resistance between X and Y for the following
circuits.
Int 2
37
Electrical Resistance
13.
a)
b)
14.
What will be the resistance of ten 20 Ω resistors when they
are connected in series?
What will be the resistance of ten 20 Ω resistors when they
are connected in parallel?
You are given the four resistors below.
1Ω, 10Ω, 100Ω, 1000Ω
a)
What is their total resistance when they are connected in series?
A
less than 1 Ω
B
between 1 Ω and 10 Ω
C
between 10 Ω and 100 Ω
D
between 100 Ω and 1000 Ω
E
greater than 1000 Ω
b)
What is their total resistance when they are connected in parallel?
A
less than 1 Ω
b) What isBtheir between
total resistance
when10they
1 Ω and
Ω are connected in parallel?
A lessCthan 1between
W
10 Ω and 100 Ω
B between
1
W
and
10
W Ω and 1000 Ω
D
between 100
C between 10 W and 100 W
E
greater than 1000 Ω
D between 100 W and 1000 W
E greater than 1000 W
15. Calculate the resistance between X and Y in the following resistor
29. Calculate
the resistance between X and Y in the following resistor networks.
networks.
a)
25 W
X
Y
b)
25 W
X
25 W
Y
25 W
100 W
100 W
Potential Divider Circuits
30. State what is meant by a potential divider circuit.
31. The following potential divider circuit was set up using the values shown.
R1
8 kW
V1
R2
12 kW
V2
10 V
a) Calculate the current in the circuit through R1 and R2.
b) Calculate the value of the potential differences (voltages) V1 and V2, across each
Int 2resistor.
V1
R1
c) Use your results to show that the relationship V = R is true.
4.
b) i) metals ii) pencil ‘lead’ is carbon
11. a) A, C, E
b) B, D, F
12. a) series
b) 0.5 A
c) 8 V
13. a) parallel
b) i) X: 0.8 A, Y: 0.5 A
c) 6 V
Electrical Resistance
14. a) I1 = 0.4 A b) V1 = 9 V, I2 = 1.5 A
c) I3 = 0.8 A, I4 = 0.8 A, V2 = 9 V
d) I5 = 1.5 A, I6 = 1 A, V3 = 4 V
15. 70 mV, 650 mV, 980 mV, 2963 mV, 3200 mV
16. 0.002 A, 0.029 A, 0.03 A, 5.805 A, 8.9 A, 120 A
17. a) current
b) 1.2 A, 0.6 A, 240 mA, 2.4 mA down the table
18. 6 W
19. 50 W
20. 0.009 A
21. 0.01 A
22. a) R = 75 W b) I = 1.8´10-4 A
c) V = 75 V d) R = 100 W
23. a) 18 V
b) 300 W
24. a) Table 1: 10, 10.3, 10.6, 12 down the table
Table 2: 10 for all entries down the table
25. a) 16 W
b) 2 kW
c) 1.6 kW
26. a) 2 W
b) 3 W
c) 9 W
d) 4 W
e) 3.6 W
f) 6.8 W
27. a) 200 W
b) 2 W
28. a) E
b) A
29. a) 45 W
b) 33 W
-4
31. a) 5x10 A or 0.5 mA
b) V1 = 4 V, V2 = 6 V
32. a) V1 = 6 V b) V1 = 3 V
33. a) V1 = 4.8 V b) V1 = 19 V
35. a) i) V1 = 0 V ii) V1 = 6V iii) V1 = 3 V b) V1 = 2 V c) RAP = 11.7 kW
Electrical Energy
37. a) 6 J
38. a) 100 W
39. a) 115 W
40. a) 18000 J
41. 50 s
42. b) 0.36 W
43. a) 1.3 A
44. b) 1920 W
45. a) 24 W
46. a) 8.7 A
47. 0.2 A
48. 60 W
50. 998 W
51. 69 W
100 W
b) 60 W
c) 3000 W
b) 6000 J
c) 1.92´106 J d) 7.2´108 J
c) 1296 J
b) 8.64´106 J
b) 48 W
b) 26 W
230
230
0.3
0.43
3A
3A
Physics: Electricity and Electronics (Int 2) – Student Material
Int 2
51
Resistance in Series
In this section you can use the equation:
Rs = R1 + R2 + R3 +......
where Rs = total resistance of a series circuit or series section of a
circuit .
1.
Three resistors R1, R2 and R3 are arranged in series as shown in the
diagram below.
R1
R2
R3
Find the missing values in the table.
(a)
(b)
(c)
(d)
(e)
(f)
2.
R1 ()
5 000
80
800
700
R2 ()
490
300
2 000
300
140
Rs ()
1 400
550
390
Calculate the total resistance of the following circuit.
5 k
3·2 k
The resistance of the following circuit is 8·8 kΩ. Calculate the
resistance of R.
950 
Int 2
100
85
225
800 
3.
R3 ()
85
25
200
R
6·3 k
Resistance in Series
Resistance
1.
(a) 5575 
(b) 405 
(c) 3000 
(d) 400 
(e) 310 
(f) 80 
2. 9 000 
3. 1 550 
Int 2
in
Series
Circuits(p.22)
Resistance in Series
Int 2
Resistance in Parallel
In this section you can use the equation
1
1 +1
1 + ....
+
=
Rp
R1 R 2 R3
where
1.
Rp
= total resistance of a parallel circuit or parallel
section of a circuit
Calculate the total resistance of each of the following circuits:
(a)
(b)
20 
80 
(e)
120 
(f)
80 
100 
400 
120 
150 
1 600 
(g)
GMV
120 
20 
80 
(d)
(c)
(h)
(i)
300 
150 
800 
600 
300
2400

Resistance in Parallel
2.
Calculate the total resistance of each of the following circuits:
(a)
(b)
(c)
600 
3 k
1·2 k
600 
3 k
600 
600 
3 k
(d)
(e)
600 
(f)
280 k
300 
3 k
560 k
600 
900 
200 
600 
560 k
3.
The total resistance of the circuit below is 80 Ω. Calculate the
resistance of R.
R
220 
1 232 
GMV
Resistance in Parallel
4. The total resistance of the following circuit is 112·5 Ω. Calculate the
resistance of resistor A.
300 
A
900 
5. The total resistance of the following circuit is 240 Ω. Calculate the
resistance of resistor X
1 200 
X
1 800 
Resistance in
1.
(a) 40 
(b) 10 
(c) 60 
(d) 48 
(e) 60 
(f) 320 
(g) 200 
(h) 100 
(i) 600 
2.
(a) 200 
(b) 1 k
(c) 240 
(d) 140 k
(e) 100 
(f) 32143 
3. 140 
4. 225 
5. 360 
GMV
Parallel
Circuits
(p.23)
Combination Circuits
Helpful Hint
Rs
=
1
Rp
1.
=
R1 + R2 + R3 +......
( for a series section of a circuit)
1 + 1 + 1 +......
R1 R2 R3
(for a parallel section of a circuit)
Calculate the total resistance in each of the following networks:
(a)
(b)
20 
60 
10 
40 
20 
60 
(c)
(d)
10 
10 
10 
10 
(e)
10 
100 
15 
15 
30 
30 
(f)
5
10 
100 
2.
10 
10 
5
The following circuit shows part of a car lighting system.
560 
250 
X
250 
Y
560 
Z
Calculate the resistance between points:
(a)
X and Y
(b)
Y and Z
(c)
X and Z.
GMV
Combination Circuits
3.
Calculate the resistance of the network of resistors shown below.
40 
80 
80 
120 
60 
4.
Which network of resistors has the lowest total resistance?
Network A
Network B
90 
90 
90 
15 
15 
90 
5. A school technician has different resistors to use in building house
wiring models.
10 
10 
50 
50 
100 
100 
He has two 10  resistors, two 50  resistors and two 100 
resistors.
How can these resistors be combined to produce a total resistance
of:
(a)
GMV
260 
(b)
300 
(c)
30 
(d)
35 ?
Combination Circuits
Combination Circuits
1.
(a) 20 
(b) 70 
(c) 25 
(d) 20 
(e) 55 
(f) 225 
2.
(a) 125 
(b) 280 
(c) 405 
3. 27429 
4. network B
5.
(a) 100
100 50
10
(b) 100
(c)
100
50
50 50
10
50
10
(d)
50
10
50
GMV
(p.25)
Miscellaneous Questions
Section 4 Miscellaneous Questions
1.
Bulbs B1, B2 and B3 are all identical. What is the voltage across bulb
B2 and bulb B3?
12 V

B1
8V

B2
B3
2.
Look at the circuit shown and find:
(a)
the voltage across R2
(b)
the current through R1.
24 V
R2
R1
16 V 
3.
In the following circuit the bulbs are identical. Find:
(a)
(b)
the voltage across each bulb
the current through each bulb.
36 V
I = 0·9 A
 12 V 
GMV
R3
I=2A
Miscellaneous Questions
4.
In the following circuit all the resistors are identical. Find:
(a)
(b)
the voltage across each resistor
the current through each resistor.
24 V
3A
A
B
C
D
5. Daral has a selection of resistors and has to combine them in some
way to obtain a total resistance of 60 .
He has two 5 , two 20  and two 90  resistors.
He sets up three different networks as shown below. Which one is
correct?
20 
20 
20 
90 
5
5
90 
Network 1
20 
Network 2
90 
5
90 
20 
Network 3
Section
1. 4 V
2.
(a) 8 V
(b) 2 A
GMV
4
Misc.
Questions(p.27)
Miscellaneous Questions
3.
(a) 24 V
(b) 03 A
4.
(a) 12 V
(b) 15 A
5. network 3
GMV
Miscellaneous Questions
2
General Level
1.
Clare has set up a circuit, as shown below, in order to switch on a
bulb.
She wants to measure the voltage across the bulb and the current
through it.
(a)
(b)
(c)
2.
What should Clare use in order to measure the voltage
across the bulb?
What should be used to measure the current in the bulb?
Redraw the circuit to show the correct positions of these
meters.
Look at the following circuits:
2V
12 
0·3 A
(a)
(b)
(c)
GMV
100 
6V
R
Calculate the voltage across the 12 Ω resistor.
Calculate the current through the 100 Ω resistor.
What is the value of resistor R?
0·015 A
Miscellaneous Questions
3.
2
An electric kettle operates at mains voltage drawing a current of
9 A.
(a)
(b)
(c)
(d)
What is the value of mains voltage?
What is the power rating of the kettle?
How much electrical energy is supplied to this kettle
each second?
How much electrical energy would the kettle use if it
was switched on for 3 minutes?
4. For each of the following circuits what should be the reading on the
ammeter and voltmeter?
(a)
2·5 V
3·6 V
(b)
A
A
05 A
10 
20 
1·2 V
V
05 A
05 A
V
1·5 V
(c)
A
0·2 A
V
GMV
Miscellaneous Questions
5.
2
Calculate the power rating of each of the following electrical
appliances.
(a)
An electric shaver which draws a current of 2 A from
the mains supply.
(b)
An electric fire which uses 5 400 000 J of energy in
30 minutes.
(c)
A lamp which operates on the mains voltage drawing a
current of 0·26 A.
(d)
A hairdryer which uses 1 080 000 J of electrical energy in
15 minutes.
6. The labels for two electrical appliances are shown below but one
important piece of information is missing from each label.
Kettle
Model No. 5510
capacity 17 litres
..............V, 50 Hz
Lamp
Model No. 50736
230 V a.c
50 Hz
.....................W
2 000 W BEEB
approved
(a)
Suggest suitable values for the operating voltage of a kettle
and the power rating of a lamp.
The flexes for these appliances are shown below:
blue
green & yellow
brown
Flex A
blue
brown
Flex B
(b)
Complete the following table for flex A.
Colour of insulation
brown
green and yellow
blue
(c)
(d)
(e)
GMV
Name of wire
What is the purpose of the green and yellow wire in flex A?
Which flex belongs to the lamp? Explain your answer.
Both the kettle and the lamp are fitted with a 3 A fuse.
Which appliance fails to operate?
Explain your answer and suggest a solution.
Miscellaneous Questions
7.
Explain how each of the following situations could result in an
accident.
(a)
(b)
(c)
Eight appliances are connected to one socket using adapters.
An electricity socket is fitted in the bathroom.
A 13 A fuse is fitted to an alarm clock/radio.
Revision Questions
General Level(p32)
2.
(a) 36 V
(b) 002 A
(c) 400 
3.
(a) 230 V
(b) 2 070 W
(c) 2 070 J
(d) 372 600 J
4.
(a) 15 A
25 V
(b) 012 A
24 V
(c) 02 A
15 V
5.
(a)
(b)
(c)
(d)
6.
(a)
2
460 W
3 000 W
598 W
1 200 W
GMV
kettle - 230 V
lamp ~ 60 W
Miscellaneous Questions
2
Credit Level
1.
A lamp is connected in parallel with a resistor as shown below. The
bulb is a 12 V, 36 W bulb.
(a)
(b)
(c)
(d)
2.
Calculate the current
through the bulb
when it is operating at
its correct voltage.
What is the resistance
of the bulb?
Calculate the current through the
resistor.
Calculate the total
current drawn from
the supply.
12 V
6
The rating plate from a hand blender is shown below.
Electronic model no. 3456
230 V 50 Hz
1 500 W
(a)
(b)
(c)
Calculate the current drawn by the blender.
Calculate the resistance of the blender.
Explain the significance of the symbol on the rating plate.
The blender has to be charged up before use. It is charged for 5
hours and the average charging current is 10 mA.
(d)
GMV
Calculate the charge stored.
Miscellaneous Questions
3.
Paul is always being accused of wasting electricity because he has
nearly every electrical appliance switched on at once in his room.
His stereo, CD player, television, lamp and computer are all
connected to the mains via an adapter as shown below.
mains
voltage
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
GMV
2
hairdryer
R = 500 
TV
R = 480 
lamp
R = 400 
computer
R = 2 k
stereo
R = 2·2 k
What kind of circuit is this?
What simple test could you carry out to prove this?
Calculate the total resistance of the circuit when all
appliances are on.
Calculate the current drawn from the mains when all the
appliances are on.
What is the power rating of the computer?
How many units of energy are used when the computer is on
for 6 hours?
If a unit of electricity is 7·4p how much does it cost to run
the computer for this length of time?
The lamp is usually on for 5 hours a day. How much money is
saved:
(i)
per day?
(ii)
per week?
if the lamp is switched off.
Miscellaneous Questions
4.
2
Junior Spark tries his hand at some DIY electrics in and around his
new home.
He designs two circuits. Circuit 1 is a model for a room light and
Circuit 2 is a model for toy car lights.
His designs are shown below.
24 V
Circuit 1
R = 900
Circuit
2
S1
S2
L1
Sidelights 12 V , 24 W
S3
L2
H1
H2
Headlights 12 V , 36 W
Look at the circuits and answer the following questions.
(a)
(b)
(c)
(d)
(e)
GMV
Describe the function of the variable resistor in circuit 1.
The variable resistor can be set at any resistance between 10 
and 10 k. Use this range to calculate the minimum and maximum
current that could flow through the bulb.
In circuit 2, which switches must be closed to switch on the head
lights?
What size of current is drawn from the battery when all the lights
in circuit 2 are on?
What is the advantage of having the sidelights and the headlights
connected in parallel instead of in series with one another?
Miscellaneous Questions
2
5. A typical toaster design consists of two heating elements arranged in
parallel as shown below.
80 
230 V
80 
Calculate the power rating of the toaster.
6.
Look at the circuit below and answer the following questions:
A
10 
S
6V
20 
(a)
(b)
(c)
(d)
7.
V
Calculate the resistance of the circuit when switch S is open.
What is the reading on the ammeter when switch S is open?
What is the reading on the voltmeter when switch S is open?
Calculate the resistance of the circuit when switch S is
closed.
Consider the following circuit.
9V
A
40 
20 
90 
(a)
(b)
(c)
GMV
60 
What is the total resistance of this circuit?
Calculate the reading on the ammeter.
What is the voltage across the 90Ω resistor?
Miscellaneous Questions
8.
2
The following circuit was set up in a classroom.
Vs
0·04A
300 
V
A
100 
P
0·03A
(a)
(b)
(c)
(d)
(e)
(f)
(g)
0·25 W
What is the current through the bulb?
Calculate the voltmeter reading.
What should the reading on the ammeter be?
Calculate the voltage across the 100Ω resistor.?
What is the voltage across the 300 Ω resistor?
What is the voltage across PQ?
Calculate the supply voltage, Vs.
Credit Level(p.36)
1.
(a) 3 A
(b) 4 
(c) 2 A
(d) 5 A
2.
(a) 652 A
(b) 3527 
(d) 180 C
3.
(c) 13266 
(d) 173 A
(e) 2645 W
(f) 016 units
(g) 1 p
(h)(i) 489 p
(ii) 3425 p
4.
(b) 22x10-3 A, 003 A
(d) 10 A
5. 1 3225 W
6.
(a) 30 
(b) 02 A
(c) 4 V
(d) 25 
GMV
Q
Miscellaneous Questions
7.
(a)
(b)
(c)
8.
(a)
(b)
(c)
(d)
(e)
(f)
(g)
GMV
36 
025 A
9 V
004
625
001
3 V
3 V
3 V
925
A
A
A
V
2
LED Resistance
Helpful Hint
When working with LED circuits you can use the equation:
V = IR
When applying this equation remember that the supply voltage is shared
between the LED and the resistor.
Example
A certain LED takes a current of 10 mA and the voltage across it is 2 V.
What should be the value of the series resistor when a supply voltage of
5 V is used?
1st. Sketch the circuit
R.
5V
R
2V
GMV
2nd. Calculate the voltage across resistor
VR
=Vsupply - Vled
=5 -2
= 3V
I = 10 mA
= 0·010 3rd. Apply V = IR to find the value of R
A
VR = 3 V
I
= 0·01 A
R = ?
VR
3
R
R
= IR
= 0·01 x R
= 3 / 0·01
= 300 
LED Resistance
2.
Use the stages outlined above to find the missing values in the
following table.
Vsupply
I
Vled
(a)
(b)
(c)
(d)
(e)
(f)
3.
R
VR
Vsupply
Voltage across Current (A)
Voltage
Resistance of
LED (V)
across R (V) R ()
(V)
6
2·0
0·010
12
2·0
0·010
8
1·8
0·016
20
1·6
0·008
4
1·5
0·020
11
2·0
0·012
For each of the following circuits calculate the value of the series
resistor which will enable the LED to operate at its ideal voltage and
current.
9V
4V
(a)
R
R
1·8 V,
12 mA
2·1 V,
10 mA
(c)
(d)
12 V
6V
R
R
2·2 V,
10 mA
GMV
1.6 V,
11 mA
(b)
LED Resistance
(e)
(f)
14 V
9·8 V
12mA
(g)
15mA
(h)
R
2 V9·5 V
R
2·3 V5 V
10mA
3 V
4.
20mA
R
R
4 V
Consider the following circuit.
5·1 V
8mA
400 
(a)
(b)
Calculate the voltage across the 400  resistor.
Calculate the voltage across the LED.
5. For the circuit shown below work out the value of the supply voltage
which will enable the LED to operate at it’s stated rating.
800 
6. The voltage and current specifications for a certain LED are 1·75 V
and 10 mA respectively. What should be the value of the series
resistor if the LED is powered by a 6 V supply?
GMV
LED Resistance
7.
Calculate the ammeter reading in the following circuit.
12 V
A
1·8 V
8.
2 040 
Calculate the voltmeter reading in the circuit shown below.
6V
8mA
475 
V
9.
What is the supply voltage
for the following circuit?
15mA
1 200 
10.
3V
Calculate the value of resistor R in the circuit below.
9V
20mA
R
4V
Section 2 - Output Devices
The L.E.D.(p.3)
GMV
LED Resistance
1. B and E
2.
(a) 4 V, 400 
(b) 10 V, 1 000 
(c) 62 V, 3875 
(d) 184 V, 2 300 
(e) 25 V, 125 
(f) 9 V, 750 
3.
(a) 190 
(b) 600 
(c) 980 
(d) 400 
(e) 1 000 
(f) 500 
(g) 650 
(h) 50 
4.
(a) 32 V
(b) 19 V
5. 11 V
6. 425 
7. 0005 A
8. 22 V
9. 21 V
10. 250 
GMV
Circuit questions
2.
The circuits below show two identical LDR’s each connected to a
6 V supply.
One LDR is placed in a cupboard and the other is placed beside a
window.
0·03 A
0·002 4 A
6V
6V
Circuit (i)
(a)
(b)
Circuit (ii)
Calculate the resistance of each LDR.
Which circuit shows the LDR in the cupboard?
3. The following circuit shows a thermistor connected to a 5 V supply
and placed in a school laboratory.
A
5V
In the morning the ammeter gave a reading of 1·25 mA. Later in the
same day the reading had risen to 2·5 mA.
GMV
(a)
Calculate the resistance of the thermistor in the morning
(b)
What happened to the temperature in the room during the
day?
Explain your answer.
Circuit questions
4.
The following information for an LDR was found in a components
catalogue.
Light Source
moonlight
60 W bulb at 1m
fluorescent
light
bright sunlight
Illumination (lux)
0·1
50
500
Resistance (k)
10 000
2·4
0·2
30 000
0·02
This LDR is connected to a 12 V supply with an ammeter in series with
it as shown in the diagram.
12 V
A
(a)
(b)
(c)
What is the resistance in ohms of the LDR when exposed to
fluorescent light?
What would the ammeter read when a lamp with a 60 W bulb
in it is placed 1 m away from the LDR?
When the ammeter gives a reading of 0·6 A which light
source is being used?
5. A pupil uses a thermistor as a simple electronic thermometer. She
connects the thermistor to an ammeter and places the thermistor
into a beaker of hot water. The ammeter gives a reading of 8 mA.
Temperature (oC) Resistance ()
6V
20
3 750
40
198
60
750
80
350
100
200
(a)
(b)
(c)
(d)
GMV
What is the temperature of the water in the beaker?
The pupil adds some more water to the beaker and the
ammeter gives a new reading of 1·6 mA. Did the pupil add hot
or cold water to the beaker?
What is the new temperature of the water?
What will the ammeter read when the water is boiling?
A
Circuit questions
Section 3 - Input Devices
Using V = I R(p.9)
2.
(a) (i) 200 
(ii) 2500 
(b) circuit (ii)
3.
(a) 4 000 
4.
(a) 02 k
(b) 0005 A
(c) bright sunlight
5.
(a) 60 0C
(b) cold
(c) 20 0C
(d) 003 A
GMV
Voltage Dividers
In a series circuit the voltage divides up between the components in the
circuit
i.e.
Vs
Vs
=
V1 + V2
R1
R2
V1 V2
where Vs = supply voltage
V1 = voltage across R1
V2 = voltage across R2
From Ohm’s law we know that since current is constant in a series circuit,
the higher the resistance of a component the greater the voltage across
it.
This idea is used in the following example to calculate the voltage across
components in a ‘voltage divider’ i.e. series circuit.
24V
Example
4
8
Use the fact that the voltage ‘split’ across each component is in the same
ratio as the resistance of each component.
V1
= R1 x Vs V2
= R2 x Vs where Rt = total resistance
Rt
Rt
= 4 x 24
= 8 x 24
12
12
= 8V
= 16 V
( Remember to check your answer e.g. does V1 + V2 = Vs )
Lastly!
e.g.
Circuit problems in electronics are usually drawn slightly
differently than you are used to seeing.
+ 24 V
24 V
4
8
8
would be
drawn as
4
0V
GMV
Voltage Dividers
Find the voltage across each resistor in the following:
(1)
+ 12 V
(2)
3
10 
6
3
0V
(5)
+ 12 V
GMV
(6)
+ 10 V
+36 V
4
20 
10 
6
16 
0V
0V
+ 24 V
(8)
+ 24 V
(9)
+ 24 V
10 
8
36 
5
4
18 
0V
(11)
+ 36 V
0V
0V
2
0V
(10)
+ 36 V
6
0V
(7)
(3)
10 
0V
(4)
+ 24 V
0V
(12) +36 V
+ 36 V
9
12 
21 
3
4
7
0V
0V
Voltage Dividers
(13)
(14) + 10 V
+ 12 V
6
40 
36 
3
120 
144 
0V
0V
0V
(16) + 5 V
(17) + 36 V
15 
36 
3 k
25 
180 
0V
(20)
+ 240 V
GMV
0V
+ 20 V
62 
22 
434 
100 
0V
0V
(18) + 24 V
2 k
0V
(19)
+ 240 V
(15)
Voltage Dividers
Helpful Hint
LDR’s and thermistors often make up part of a voltage divider circuit in
electronic systems.
It is important to remember that the resistance of these components
varies with external conditions.
The following tables indicate how the resistance of an LDR and
thermistor vary with external conditions.
LDR
Thermistor
Thermistor
Thermistor
Light condition
Resistance ()
dark
10 000
light
2 500
bright
20
o
Temperature
Temperature ((oo C)
C)
Temperature ( C)
10
10
10
40
40
40
100
100
100
Resistance
Resistance ()
()
Resistance ()
4
4 000
000
4 000
11 980
980
1 980
200
200
200
Use the information above to solve questions 21 - 24.
21. The following circuit is part of the input to an electronic frost alarm.
+ 230 V
100 
If the circuit operates from mains
voltage calculate the voltage drop
across the thermistor when it is
(a)
(b)
10 o C
40 o C
0V
22. The following circuit could be part of a light meter for a camera.
Use the information above to find
the voltage
drop across the LDR when it is:
+ 12 V
1 k
0V
GMV
(a)
(b)
dark
light
Voltage Dividers
23.
Calculate the voltage across the resistor in the following circuit
when the temperature is:
(a)
(b)
+ 24 V
o
100 C
40 o C
500 
0V
24.
A young engineer designs part of an electronic system to trigger an
alarm when it gets too bright.
What will the ‘trigger voltage’ across the resistor be in the
following system when it is ‘bright’?
+ 36 V
1·5k
0V
25. At what temperature would the following circuit show equal readings
on each voltmeter?
+ 230 V
V1
200 
0V
GMV
V2
Voltage Dividers
Helpful Hint
In a circuit like the following:
+5V
R1
X
R2
0V
You are often required to calculate the voltage( or potential) at X
This is the same as asking for the voltage (or potential) across
resistor R2
Calculate the voltage at X in questions 26 - 30.
26.
27.
+ 12 V
28.
+5V
20
+ 36 V
65
X
0V
1 k
X
X
0V
Switch S open
0V
Capacitor C uncharged
29.
Switch S closed
30.
+5V
+12 V
3·5 k
X
0V
Capacitor C fully charged
GMV
X
0V
10 k
Switch S open.
Voltage Dividers
Voltage Dividers(p.13)
1. 6 V, 6 V
2. 12 V, 12 V
3. 18 V, 18 V
4. 2 V, 10 V
5. 4 V, 6 V
6. 20 V, 16 V
7. 16 V, 8 V
8. 16 V, 8 V
9. 16 V, 8 V
10. 27 V, 9 V
11. 27 V, 9 V
12. 27 V, 9 V
13. 8 V, 4 V
14. 25 V, 75 V
15. 48 V, 192 V
16. 2 V, 3 V
17. 135 V, 225 V
18. 4 V, 20 V
19. 30 V, 210 V
20. 36 V, 164 V
21.
(a) 22439 V
(b) 21894 V
22.
(a) 1091 V
(b) 857 V
23.
(a) 1714 V
(b) 484 V
24. 3553 V
25. 100 0C
26. 12 V
27. 0 V
28. 0 V
29. 5 V
30. 0 V
GMV
Voltage Dividers
1.
The circuit below is set up in a laboratory.
A
D
C
(a)
(b)
(c)
(d)
B
Name components A, B, C and D.
Explain why component C is necessary in this circuit.
Why is it important that component B is connected the right
way round?
Light emitting diodes can be arranged as follows to produce
different numbers:
What is the name given to this arrangement of LED’s?
2.
Look at the following circuits:
X
(a)
(b)
(c)
(d)
(e)
GMV
Y
Name components X and Y.
What will happen to the resistance of component X as the
temperature increases?
What will happen to the current flowing in X as the
temperature increases?
What will happen to the resistance of component Y as it gets
dark?
What will happen to the current flowing in Y as it gets dark?
Voltage Dividers
3.
The resistance of a certain thermistor was recorded at various
temperatures. The results are shown in the table below.
Temperature (oC)
10
40
100
Resistance ( )
4 000
1 980
200
The thermistor was then connected to a 4 V battery and ammeter
and exposed to the same range of temperatures
4V
A
(a)
What was the ammeter reading when the temperature was 10 0C?
(b)
What temperature is indicated by an ammeter reading of 0·02 A?
General Level(p.34)
3.
(a) 0001 A
(b) 100 0C
4.
(b) D
(c) A
5.
(a) 25
(b) 0005
(c) 4 V
GMV
29.
b)
a)a) resistance between X25
b) resistor networks.
25
W Y in the following
25
25
Calculate the
and
W
25 W
W
25WW
X
Y
X
X
Y
X
a)
b)
25 W
25 W
2525
25
WWW
X
Y
X
Y
a)
b)
25 W
100 W
W
25 W
25 W
25 W 100
100
100WW Y
X
Y
X
Voltage Dividers
100 W
100 W
25 W
100 W
YY
100 W
Potential
Divider
Circuits
Potential
Divider
Circuits
Potential
Divider
Circuits
30. State
State
what
meant
by
potentialdivider
divider circuit.
1.
State
what
is meant
byby
a potential
circuit.
Potential
Divider
Circuits
30.
what
isismeant
aa potential
divider
circuit.
30.
State Divider
what is meant
by a potential divider circuit.
Potential
Circuits
31.
The
following
potential
divider
circuitwas
wasset
set
shown.
potential
divider
circuit
up
usingthe
thevalues
values
31.
The
following
potential
divider
circuit
was
set up
up using
using
the
values
shown.
30. 2.StateThe
whatfollowing
is meant
by
a potential
divider
circuit.
31. The following
potential
divider
circuit
was
set
up
using
the
values
shown.
shown.
31. The following potential divider circuit was set up using the values shown.
R1
8 kW
10
V
10 V 8 kW
R1
10 V
10 V
R2
R2
R1
R
1
R2
R
2
12 kW
12 kW
88 kW
kW
V
V11
V1
12
12 kW
kW
V2
V
V22
V1
V2
Calculate the
the current
current in
in the
the circuit
circuit through
through R
R .
a)a) Calculate
R11 and
and
a)
Calculate
the
current
incircuit
the circuit
through
R.1 and
R2.R22.
a) Calculate
the
current
in
the
through
R
and
R
1 differences
2
Calculate the
the value
value of
of the
the potential
potential
(voltages)
1 and
2,,across
b)b) Calculate
differences
(voltages)VV
V
andVVV
acrosseach
each
1
2
b)
Calculate
the
value
of
the
potential
differences
(voltages)
and
,
1
2
b)a) Calculate
value
of in
thethe
potential
differences
(voltages)
Calculatethe
the
current
circuit through
R1 and
R2. V1 and V2, across each
resistor.
resistor.
across each
resistor.
b) resistor.
Calculate
the value
of the potential differences (voltages) V1 and V2, across each
V
R
c) Use your
results
showtothat
true.
V1
R1 istrue.
Useyour
yourto
results
showthe
that relationship
the relationship
relationship
resistor.
V1
R1 V21 == R21 is
c)c) Use
results
to show
that
the
is
true.
R2
c) Use your results to show that the relationship V = R isVtrue.
2
V21
R21
d)c) Use
Useyour
yourresults
results
to show
that
the relationship
=
to show
that the
relationship
true. R
R11 VS is also true.
V2
R2 is
d)
Use
your
results
to
show
that the
the relationship
relationship
1=
R1 V
d)
Use
your
results
to
show
that
V
=
VS is also true.
R
1V
d) Use your results to show that the relationship V1 =
is11+R
also
+R22 true.
S R
R
+R
1 R1 2
is also
d) Use
yourtrue.
results to show that the relationship V1 =
V is also true.
R1+R2 S
32. Calculate
Calculatethe
the value
value of
of V
V1 in
in the
the following
following circuits.
32.
circuits.
1
32. 3.Calculate
the value
V1 inof
theVfollowing
circuits.
Calculate
theofvalue
1 in the following circuits.
32. Calculate the
value of V1 in the following circuits.
b)
a)a)
b)
a)
b)
6 kW
3V
4 kW
24 V
3V
24 V
6 kW
36VkW
4 kW
244VkW
a)
b)
6 kW
12 kW
12 kW
3V
12 kW
12
V1kW
4 kW
V
V11
24 V
500 W
W
V500
1
500 W
500 W
V1
V1
V1
V1
33. Calculate the value of V1 in the following circuits.
4. Calculate the value of V1 in the following circuits
a)
b)
Physics:
Electricity
and Electronics (Int 2) – Student Material 250 W
15Electricity
kW
Physics:
and(Int
Electronics
(IntMaterial
2) – Student Material
Physics: Electricity
and
Electronics
2) – Student
Physics: Electricity
and Electronics (Int 2) – Student Material
12 V
10 kW
V1
39
39
20 V
5 kW
V1
5. A fixed 6 V d.c. power supply has to be reduced to give constant
34. A fixed
6 V d.c.
supplyahas
to be reduced
to give constant output of 1.5 V using a
output
of power
1.5 V using
potential
divider.
potential
divider.
Design
a potential divider circuit that will give a constant output of
Design
a
potential
divider
that will give a constant output of 1.5 V from the 6 V
1.5 V from the
6 Vcircuit
supply.
supply.
35. A 20 kW potentiometer AB is connected across a 6V d.c. power supply as shown below.
GMV
B
39
39
34.
A fixed 6 V d.c. power supply has to be reduced to give constant output of 1.5 V using a
potential divider.
Voltage
Design a Dividers
potential divider circuit that will give a constant output of 1.5 V from the 6 V
supply.
NUMERICAL ANSWERS
6. A 20 kΩ potentiometer AB is connected across a 6V d.c. power
35. A
20 supply
kW potentiometer
is connected across a 6V d.c. power supply as shown below.
as shown AB
below.
Circuits
2.
3.
4.
11.
12.
13.
14.
a) 240 C
b) 7.3 A
a) 144 000 C b) 72 000 s or 20 hours
c) constant current
B
b) i) metals ii) pencil ‘lead’ is carbon
a) A, C, E
b) B, D, +
F
a) series
b) 0.5 A 6 V c) 8 V
20 kW
a) parallel
b) i) X: 0.8
A,
Y:
0.5 A P c) 6 V
V1
a) I1 = 0.4 A b) V1 = 9 V, I2 = 1.5 A
A d) I = 1.5 A, I = 1 A, V = 4 V
c) I3 = 0.8 A, I4 = 0.8 A, V2 = 9 V
5
6
3
15. 70 mV, 650 mV, 980 mV, 2963 mV, 3200 mV
The sliding contact, P, can be moved to any point along the potentiometer AB.
16. The
0.002sliding
A, 0.029
A, 0.03 P,
A, can
5.805
8.9 A, 120
A point along the
contact,
beA,moved
to any
17. a) current
b) 1.2 A, 0.6 A, 240 mA, 2.4 mA down the table
potentiometer
AB. voltage, V1, when the sliding contact, P, is at
a) What
will be the output
18. 6 W
i) position
A
19. a)
50 WWhat will be the output voltage, V1, when the sliding contact, P,
ii) position
at A B
20. is0.009
iii) midway
between A and B?
21. 0.01 Ai) position A
b) What would be the output voltage,
V , if the sliding contact P was one third of the
22. a) R ii)
= 75
W b) I = 1.8´10-4 A 1
c) V = 75 V d) R = 100 W
positionB
length along the potentiometer from A?
23. a) 18iii)
V midway
b) between
300 W
A and B?
c) What would
be the resistance
between
points A and P if the potentiometer was
24. b)
a) Table
1:
10,
10.3,
10.6,
12
down the
table V , if the sliding contact P
What
would
be
the
output
voltage,
1
adjusted to give an output voltage of 3.5V?
Table 2: 10 for all entries down the table
was one third of the length along the potentiometer from A?
25. a) 16 W
b) 2 kW
c) 1.6 kW
would
between
26. c)
a) 2 What
W
b) 3be
W the resistance
c) 9 W
d) 4 Wpoints A
e) and
3.6 P
W if thef) 6.8 W
potentiometer
27. a) 200
W
b) 2 W was adjusted to give an output voltage of 3.5V?
28. a) E
b) A
29. a) 45 W
b) 33 W
-4
31. a) 5x10 A or 0.5 mA
b) V1 = 4 V, V2 = 6 V
32. a) V1 = 6 V b) V1 = 3 V
33. a) V1 = 4.8 V b) V1 = 19 V
35. a) i) V1 = 0 V ii) V1 = 6V iii) V1 = 3 V b) V1 = 2 V c) RAP = 11.7 kW
Electrical Energy
37. a) 6 J
38. a) 100 W
b) 60 W
c) 3000 W
39. a) 115 W
6
8
40.Electricity
a) 18000
J
b) 6000
c) 1.92´10
Physics:
and Electronics
(Int 2)J – Student
Material J d) 7.2´10 J
41. 50 s
42. b) 0.36 W
c) 1296 J
43. a) 1.3 A
b) 8.64´106 J
44. b) 1920 W
45. a) 24 W
b) 48 W
46. a) 8.7 A
b) 26 W
47. 0.2 A
48. 60 W
50. 998 W
51. 69 W
230
0.3
3A
100 W
230
0.43
3A
GMV
Physics: Electricity and Electronics (Int 2) – Student Material
40
51
Voltage Dividers
ELECTRONIC COMPONENT PROBLEMS
ELECTRONIC
COMPONENT
1.
Draw the
symbols for PROBLEMS
ELECTRONIC COMPONENT PROBLEMS
a) a relay switch
74. Draw the symbols for
b) Draw
a loudspeaker
the symbols for
a) 74.
a relay switch
c) a)
an LED.
a relay switch
b) a loudspeaker
b)
c) an LED. a loudspeaker
an LED.
2. Why c)
must
a resistor be connected in series with a light emitting
75. Why
mustwhen
a resistor
be aconnected
in series with a light emitting diode when using a 5 V
diode
using
5 V supply?
75.
Why
must
a
resistor
be
connected
in series with a light emitting diode when using a 5 V
supply?
supply?
3. An LED and resistor are connected in series to a 5 V supply as
76. An LED and resistor are connected in series to a 5 V supply as shown. The maximum
shown.
maximum
allowed
current
is as
12shown.
mA. The
76.
AnThe
LEDthrough
and resistor
are connected
in through
series
to athe
5are
V LED
supply
The maximum
allowed
current
the LED
is 12 mA. The
voltages
given.
voltages
arecurrent
given.through the LED is 12 mA. The voltages are given.
allowed
A
A
3V
3V
2V
2V
B
B
0 to
V be
areconnected
to be connected
to the
circuit.
Which
will be
a) a)
+5 V +5
andV0and
V are
to the circuit.
Which
will be
connected
to A and
a)
+5 Visand
0light?
VAare
connected
andtoBbeifconnected
the LEDtoisthe
to circuit.
light? Which will be connected to A and
B if the
LED
toto
Bthe
if the
LEDmaximum
is to
light?through
Calculate
the
currentthe
through
b) b)
Calculate
maximum
current
resistor.the resistor.
b)
Calculate
the
maximum
current
through
the resistor.
is theofvalue
of the
resistor
needed
protect the LED?
c) c)
WhatWhat
is the value
the resistor
needed
to protect
the to
LED?
c) What is the value of the resistor needed to protect the LED?
LED
is connected
as shown
the following
data
foristhe
LED is
77.4. An An
LED
is connected
as shown
and theand
following
data for the
LED
shown.
77.
An LED Viss connected
as shown and the following data for the LED is shown.
shown.
= 3V
Vs = 3 V
R
R
Imax = 20 mA
Vmax = I1max
V = 20 mA
Vmax = 1 V
Calculate the least value of resistance of the resistor R, placed in series with the LED,
the
value
ofresistance
resistance
of resistor
the resistor
R, placed
Calculate
the
least
value
of
of the
R, placed
in seriesinwith the LED,
whichCalculate
would
allow
itleast
to
work
properly.
series
with
theallow
LED,itwhich
would
allow it to work properly.
which
would
to work
properly.
78. Calculate the following protective resistors from the following data.
following
protective
resistors
thethe
following
data.data.
Vs =Calculate
6 Vthe the
LED
(Vmax
= 1.5 V resistors
Imax =from
50 mA).
5. a) 78.
Calculate
following
protective
from
following
a)
V
=
6
V
LED
(V
=
1.5
V
I
=
50
mA).
b) a)
VsVs= = 10
LED
(Vmax
= Imax
2.0
Imax = 100
max V = 50mA).
max mA).
6VsVLED
(Vmax
= 1.5V
VVs = LED
10 V (VLED
(V
=
2.0
V
I
= 100 mA).
c) b)
VsVs=b)= 510V
=
1.5
V
I
=
50
maxmA).
max
LED (Vmax
= 2.0Vmax
Imax = max
100mA).
c) Vs = 5 V LED (Vmax = 1.5 V Imax = 50 mA).
c) Vs = 5V LED (Vmax = 1.5V Imax = 50mA).
79. State what happens to the resistance of:
State what
happens
the resistance
of:
a) 79.
a thermistor
subjected
to to
increasing
temperature
a)
a
thermistor
subjected
to
increasing
temperature
6. b) anState
what
happens
to
the
resistance
of:
LDR as the light intensity falling on it increases.
LDR as the light
intensitytofalling
on it increases.
a) b) aanthermistor
subjected
increasing
temperature
b)
an LDR as the light intensity falling on it increases.
GMV
Physics: Electricity and Electronics (Int 2) – Student Material
47
Voltage Dividers
7.
a)
A thermistor is connected in series to a resistor is connected
to a 5 V supply as shown. What will happen to the output voltage
as the temperature of the thermistor rises?
b) What difference would there be to the output voltage if the
thermistor and the 4 kΩ resistor were interchanged?
or is connected in series to a resistor is connected to a 5 V supply as
hat will happen to the output voltage as the
+5 V
80. a) A thermistor is connected in series to a resistor is connected to a 5 V supply as
re of the thermistor rises?
80. a) A thermistor is connected in series
to a resistor is connected to a 5 V supply as
shown. What will happen to the4 kW
output
voltage as the
+5 V
shown. What will happen to the output voltage as the
+5 V
of the thermistor rises?
erence would there be to thetemperature
output voltage
4 kW
temperature of the thermistor rises?
4 kW
mistor and the 4 k W resistor were interchanged?
Vout
b)b)What
therebebetotothetheoutput
output
voltage
Whatdifference
difference would
would there
voltage
if ifthe
the440kkVWWresistor
resistor
were
interchanged?
thethermistor
thermistor and
and the
were
interchanged?
current and voltage reading in the following circuits.
Vout
Vout
0V 0V
Calculatethe
thecurrent
current and
and voltage
reading
in in
thethe
following
circuits.
81.81. Calculate
reading
following
circuits.
c) voltage
8. Calculate the current
and voltage reading in the following circuits.
b)
a) a)
A
V
2 kW
5V
2 kW
0V
2 kW
6V
8
kW
6 V0 V
0V
4 kW
4 kW
V
d)
V
6 kWA
10 V
0V
V
8 kW
V
V
V
V
6 kW
10 V
0 V 10 V
A
6 kW
0 V 4 kW
V
4 kW
V
A
A
e)
V
V
2 kW
f)
12 d)
V
V
0 V 15
7 kW
0V
15 V 1 kW 5 kW
0V
5 kW
A
A
V
A
2 kW
A 7 kW
c) c)
2 kW
5V
05VV 4 kW
0V
8 kW
A
e)
A
b)
b)
e)5 V 12 V
0V
2 kW
12 V 7 kW1 kW
0V
1 kW
0V
A
f)
3 kW A
2 kW
3 kW A
f)
5V
0V
VV
3 kW
5 V 7 kW
0V
V
V
7 kW
V
nnected to a 5 kW resistor
asLDR
shown.
82. An
is connected to a 5 kW resistor as shown.
9. An
LDR
to
5. kΩ resistor
The values
of its
The
valuesisofconnected
its
for aparticular
conditionsas
areshown.
shown below
.
its resistance for particular
conditions
areresistance
shown below
82. Anresistance
LDR is connected
to
a
5
kW
resistor
as
shown.
for particular conditions are shown below.
V shown below .
The values of
its
resistance
for particular conditions+5are
+5
V
Resistance
Condition
dition
Resistance
ht
100 W
k
20 kW
100 W
Light
100 W
5 kW
Light
Dark
+5 V
Resistance
20 kW
Dark
Condition
0V
20 kW
5 kW
Vout
What will be the output voltage when the LDR is
he output voltage when the
is b) in sunlight?
a) inLDR
the dark
Vout
0V
5 kW
Vout
0V
b) in sunlight?
willLDR
be the
output voltage
the LDR
is in series with a 1 kW resistor.
83. What
a) An
of resistance
100 kWwhen
in darkness
is placed
What will be the output voltage when the LDR is
a)
in
the
dark
b)
in
sunlight?
The
supply
voltage
is
6
V
d.c.
f resistance 100 kW in darkness
isthe
placed
in series with a 1 kW resistor.
a)i) inDraw
dark
the
above
circuit.
y voltage is 6 V d.c.
ii)in
Calculate
the voltage
across
each
component.
sunlight?
83. a) b)
An
LDR
of resistance
100
kW in
darkness
is placed in series with a 1 kW resistor.
he above circuit.
The supply voltage is 6 V d.c.
ate the voltage across each
b) component.
LDR is placed in the light giving it a resistance of 4 kW.
i) The
Draw
the above circuit.
Calculate the new voltage cross each component.
ii)
Calculate
is placed in the light giving it a resistancetheofvoltage
4 kW. across each component.
C
the new voltage cross
component.
84.each
The
diagrams opposite show two different
b)
The
LDR
is placed in the light giving it a resistance of 4 kW. A
types
of
transistors.
GMV
C
Calculate
the
new
voltage
cross each component.
C A
a) Copy and name
each
symbol.
opposite show two different
B
b) Label points A, B and C.
istors.
A
C
C
B
C
Condition
Light
Dark
+5 V
Resistance
100 W
Voltage
20 kW Dividers
5 kW
10.
a)
Vout
An LDR of resistance
100 kΩ in darkness is placed in series with
0V
a 1 kΩ resistor. The supply voltage is 6 V d.c.
hat will be the output voltage when
LDRthe
is above circuit.
i) the
Draw
in the dark b) in sunlight?
ii) Calculate the voltage across each component.
An LDR of resistance 100 kW in darkness is placed in series with a 1 kW resistor.
The supply voltage is 6 b)
V d.c.The LDR is placed in the light giving it a resistance of 4 kΩ.
i) Draw the above circuit. Calculate the new voltage cross each component.
ii) Calculate the voltage across each component.
11. The diagrams opposite show two different types of transistors.
The LDR is placed in the
giving
it aname
resistance
4 kW.
a)lightCopy
and
eachofsymbol.
Calculate the new voltage
cross
each
component.
b) Label points A, B and C.
C
C
e diagrams opposite show two different
pes of transistors.
A
A
Copy and name each symbol.
B
B
Label points A, B and C.
cuit which automatically switches on in light conditions is shown with one
85. 12.A(Int
circuit
whichMaterial
automatically
switches
on in light
is
one
automatically
switches
onconditions
in light conditions
is shown
Electricity
and Electronics
– Studentwhich
48shown with
rtant component
missing A2)circuit
important component missing
with one important component missing
5V
5V
0V
0V
opy and complete thea)diagram,
adding
thecomplete
missing
component.
a)
and
the diagram,
adding
the
missing component.
Copy Copy
and
complete
the diagram,
adding the
missing
component.
xplain how the circuitb)works.
b)
Explain
how
the works.
circuit works.
Explain
how the
circuit
ircuit below shows
a The
temperature
sensing
device.
86. 13.
circuit
below
shows
a temperature
sensing device.
The
circuit
below
shows
a temperature
sensing device.
5V
5V
1 kW
1 kW
a)the base-emitter
Calculate the
voltage
across the base-emitter of the
alculate the voltage across
of the
transistor:
a) Calculate
the voltage
across
the base-emitter of the transistor:
transistor:
) in the cold when the resistance
the thermistor
is 9 kW. of the thermistor is 9 kW.
i) in theofcold
when the resistance
°
i)
in
the
cold
when
the resistance of the thermistor is 9 kΩ
°
) at 100 C when its resistance
is 1 kW.
ii) at 100
C when its resistance is 1 kW.
ii) at 100 °C when its resistance is 1 kΩ
ence explain how theb)
circuit
works.
Hence
explain how the circuit works.
b) Hence
explain how the circuit works.
ow could you alter thec)sensitivity
of the
How could
youdevice?
alter the sensitivity of the device?
c) How could you alter the sensitivity of the device?
gn a circuit which
allowa an
LEDwhich
to light
whenallow
it getsantoo
dark.
87.would
Design
circuit
would
LED
to light when it gets too dark.
the energy changes
the the
following
devices.
88. for
State
energyinput
changes
for the following input devices.
microphone b) a thermocouple
c) ab)
solar
cell.
a) a microphone
a thermocouple
c) a solar cell.
GMV
the purpose of an
89.amplifier.
State the purpose of an amplifier.
four examples of
systems
that use
amplifiers.systems that use amplifiers.
90.electronic
Give four
examples
of electronic
Voltage Dividers
14.
Design a circuit which would allow an LED to light when it gets too
dark.
15.
State the energy changes for the following input devices.
a) a microphone
b) a thermocouple
c) a solar cell.
16.
State the purpose of an amplifier.
17.
Give four examples of electronic systems that use amplifiers.
18.
Explain why a good audio amplifier should only increase the amplitude
of the input signal and not the frequency.
19.
State the expression for the voltage gain of an amplifier.
20. An amplifier has a gain of 20. Calculate the output voltage if the
input voltage is 200 mV.
21.
Find the unknown values using the
amplifier.
a) Gain=200
Vin=5mV
b) Gain=?
Vin=10mV
c)
Gain=200
Vin = ?
expression for the gain of an
Vout =?
Vout =5V?
Vout =1.5V
95.22.Describe
howhow
the voltage
gain ofgain
the amplifier
shown below
could
be measured
Describe
the voltage
of the amplifier
shown
below
could be
experimentally.
measured experimentally.
CD
Amplifier
Player
Your description should include
i) a diagram showing any extra apparatus required
Your description should include
ii) the measurements taken
i)
a diagram showing any extra
apparatus
required
iii) how
you would
use these measurements to
ii)
the measurements takencalculate the gain. (Note the input and output will be
iii)
how you would use thesea.c.).
measurements to calculate the gain.
(Note the input and output will be a.c.).
GMV
g) 1000 turns
g) 0.1 A
h) 3680 turns
h) 50 turns
i) 24 V
i) 500 turns
Voltage Dividers
Electronic Components
76. a) A - +5 V B - 0 V
b) 12 mA
c) 250 W
77. 100 W
78. a) 90 W
b) 80 W
c) 70 W
81. a) 0.001 A,
4V
b) 0.0005 A, 1 V
c) 0.001 A,
4V
d) 0.00125 A, 8.75 V
e) 0.004 A,
4V
f) 0.0005 A,
3.5 V
82. a) 1 V
b) 4.9 V
83. a) LDR - 5.9 V R - 0.1 V
b) LDR - 4.8 V R - 0.2 V
86. a) i) 0.5 V
ii) 2.5 V
93. 4 V
94. a) 1 V
b) 500
c) 0.0075 V
Physics: Electricity and Electronics (Int 2) – Student Material
GMV
52
Voltage Dividers
GMV
Electrical Measurements
GMV