A-Level Physics · guided topic map
Electric circuits for Cambridge International AS & A Level Physics
Electric circuits for A-Level Physics, organized into 3 syllabus topics and 13 mapped concept guides.
- Syllabus topics
- 3
- Mapped concept guides
- 13
- Educational level
- Cambridge International AS & A Level
Syllabus to lesson
Choose the exact concept
Work in order or jump to the concept named in your specification, course outline, or assignment.
9Electricity
AS Level foundations
7 guides+
Electricity
AS Level foundations
- 01Electric current and charge carriersMapped lesson
- 02Potential difference and energy per chargeMapped lesson
- 03Electrical powerMapped lesson
- 04Resistance, Ohm's law, and I-V graphsMapped lesson
- 05ResistivityMapped lesson
- 06Non-ohmic componentsMapped lesson
- 07Thermistors and light-dependent resistorsMapped lesson
10D.C. circuits
AS Level foundations
5 guides+
D.C. circuits
AS Level foundations
- 01Practical circuit symbols and diagramsMapped lesson
- 02E.m.f. and internal resistanceMapped lesson
- 03Kirchhoff's lawsMapped lesson
- 04Potential dividers and sensorsMapped lesson
- 05Potentiometer circuits and null methodsMapped lesson
21Alternating currents
A Level extension
1 guide+
Alternating currents
A Level extension
- 01Alternating currentsMapped lesson
Diagrams
Electric circuits as A-Level Physics draws it
The figures from the A-Level Physics practice papers that sit on these syllabus points — the apparatus, circuits and graphs an exam question actually puts in front of you.
01Fig. 10.1Electricity · D.C. circuitsA Level
Figure comment
Fig. 10.1A single series loop. Along the bottom, a cell with its long plate on the left and a small resistor labelled r sit together inside a dashed rectangle labelled battery, the cell marked e.m.f. 12.0 V. From the dashed box the wire runs to the left, up the left-hand side and along the top through a resistor labelled R that has an arrow drawn across it to show that it is variable, then down the right-hand side through a circle marked A, and back along the bottom into the box. An arrow on the top wire labelled I shows the direction of the conventional current.
Read the comment once, then trace every arrow, label, axis or component in the drawing before opening the questions.
Guided questions 5 parts
Reading cue. r sits inside the dashed box with the cell, so read the box as the whole source, and read 12.0 V as labelling that source, not the p.d. across its terminals.
aState The ammeter reads 2.0 A. State the current in the resistor r inside the dashed box, and give the reason from Fig. 10.1.
Check answer 2 marks
- 2.0 A
- the components form a single series loop, so the current is the same at every point in it
bCalculate With R set to 4.0 Ω the ammeter reads 2.0 A. Calculate the charge that passes through the ammeter in 5.0 minutes, and the energy delivered to R in that time.
Check answer 3 marks
- Q = It = 2.0 × 300 = 6.0 × 10² C
- p.d. across R = 2.0 × 4.0 = 8.0 V
- energy = VQ = 8.0 × 600 = 4.8 × 10³ J
cDetermine The internal resistance of the battery is 2.0 Ω. Determine the setting of R that makes the ammeter read 1.5 A.
Check answer 3 marks
- e.m.f. = I(R + r), so 12.0 = 1.5 × (R + 2.0)
- R + 2.0 = 8.0 Ω
- R = 6.0 Ω
dDeduce A second identical battery is connected in series with the first in the loop of Fig. 10.1, with R left at 4.0 Ω. Deduce whether the ammeter reading doubles.
Check answer 4 marks
- total e.m.f. = 24.0 V
- total resistance = 4.0 + 2.0 + 2.0 = 8.0 Ω
- I = 24.0 / 8.0 = 3.0 A
- the reading rises from 2.0 A to 3.0 A, not to 4.0 A, because the internal resistance in the loop has doubled as well
Transfer challenge
A 12 V car battery of internal resistance 0.020 Ω delivers 150 A to a starter motor. Calculate the terminal potential difference of the battery while the motor is turning, and explain why the headlamps dim at that moment.
Check answer 3 marks
- lost volts = Ir = 150 × 0.020 = 3.0 V
- terminal p.d. = 12 − 3.0 = 9.0 V
- the lamps are connected across the terminals, so the p.d. across them falls and they are less bright