12 Marking scheme: Worksheet
1 The same and equal to 2.0 A.
[1]
2 Rtotal =
R1 R2
R1 + R2
and
Rtotal =
R2 R
=
2R 2
The total resistance is half that of one of the resistors.
3 a
R1 = R2 = R
[1]
R = R1 + R2 = 10 + 30 = 40 Ω
b R=
R=
c
[1]
R1 R2
R1 + R2
[1]
10 × 30
= 7.5 Ω
10 + 30
[1]
10 × 10
= 5.0 Ω
10 + 10
Combining with the 10 Ω resistance in series: R = R1 + R2 = 10 + 5.0 = 15 Ω
[1]
R = R1 + R2 = 100 + 220 = 320 Ω
[1]
Resistance of the parallel section: R =
4 a
b I=
c
5 a
V 6 .0
=
R 320
[1]
[1]
V = IR = 1.875 × 10−2 × 220
V = 4.13 V ≈ 4.1 V (I = same)
[1]
[1]
R1 R2
68 × 120
Ω
=
R1 + R2 68 + 120
[1]
R = 43.4 Ω ≈ 43 Ω
[1]
V
1 .5
=
R 43.4
I = 3.46 × 10 −2 A ≈ 3.5 × 10 −2 A (35 mA)
[1]
I=
1
6
[1]
I = 1.88 × 10 −2 A ≈ 1.9 × 10 −2 A (19 mA)
R=
b
[1]
Rtotal
1
Rtotal
R total
=
[1]
1
1 1
+ +
2R R R
[1]
1+ 2 + 2
5
=
2R
2R
2R
=
(or R total = 0.4 R )
5
[1]
=
[1]
7 a
9.0 = 2.0 + V
V = 9.0 − 2.0 = 7.0 V
b Current in LED = current in resistor
V 7 .0
I= =
= 0.070 A
R 100
c P = VI = 9.0 × 0.07
P = 0.63 W
COAS Physics 1 Teacher Resources
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[1]
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Original material © Cambridge University Press 2005, 2008
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12 Marking scheme: Worksheet
8 a
1.57
= 0.262 A
6
P
60
V= =
I 0.262
Current in each lamp =
[1]
P = VI so
[1]
V = 230 V
b
R=
[1]
V
230
=
I 0.262
[1]
[1]
R ≈ 880 Ω
9 Maximum resistance, Rmax = 1.1 × (22 + 10) = 35.2 Ω
Minimum resistance, Rmin = 0.9 × (22 + 10) = 28.8 Ω
V
12
Imin =
= 0.341 A
=
Rmax 35.2
V
12
Imax =
= 0.417 A
=
Rmin 28.8
[1]
[1]
[1]
[1]
The current can be any value between 0.34 A and 0.42 A.
10 Voltmeter has infinite resistance:
6 .0
I=
= 1.0 × 10−5 A
3
(100 + 500) × 10
[1]
V = IR = 1.0 × 10−5 × 500 × 103 = 5.0 V
[1]
The student would expect a reading of 5.0 V.
Voltmeter has resistance of 220 kΩ:
220 × 500
= 153 kΩ
R=
220 + 500
The resistance of the parallel combination is 153 kΩ.
I=
6 .0
= 2.37 × 10−5 A
(100 + 153) × 103
[1]
[1]
V = IR = 2.37 × 10 −5 × 153 × 10 3 = 3.63 V ≈ 3.6 V
[1]
The actual reading on the voltmeter is 3.6 V. In practice, voltmeters ‘load’ circuits and give
a reading less than the expected value.
COAS Physics 1 Teacher Resources
Original material © Cambridge University Press 2005, 2008
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