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Electrical
circuits: 2.4
More problem solving by directly comparing
simple circuit diagrams
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Dr Phil Brown PhD:
Doc Brown's physics exam revision notes suitable for students of UK
IGCSE & GCSE level physics courses, ~ US grades 9-10 physics, updated
May 27th 2025]
Make sure you know your electrical circuit
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[ KEY
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INDEX for physics notes on
drawing and interpreting simple electrical circuits
This page contains online questions only. Jot down
your answers and check them against the worked out answers at the end of
the page
ANSWERS to ALL the QUESTIONS at the end of the page
2.4 (Set A) More problem solving by directly comparing
simple circuit diagrams
(some simple current deductions or calculations)
Unless otherwise stated, the bulbs are identical
resistors and the individual cells (batteries) are identical
too.
The cell/lamp ratio is equal to the p.d/resistance
ratio (or vice versa). p.d. = potential difference in volts.
Lamp resistance are added together when wired in
series.
Similarly, the total p.d. (voltage) equals the sum
of the cells when wired in series.
Q1.
From the four circuits shown:
(a) In which two circuits will the bulb/bulbs be the same brightness?
(b) In which circuit/circuits will the lamps glow
the dimmest?
(c) In which circuit/circuits will the lamps glow
the brightest?
ANSWERS
Q2.
From the four circuits shown
(a) Which two circuits will have the same
brightness?
(a) Which circuit will have the brightest lit lamp or lamps'?
(c) Which circuit will have 'the dimmest lit
lamp/lamps?
ANSWERS
Q3.
From the four circuits shown:
(a) In which two 'will the lamps be the same brightness'?
(b) Which circuit/circuits will have the brightest
lit lamp/lamps?
(c) Which circuit will have the dimmest lamp/lamps?
ANSWERS
Q4.
The five circuits show various arrangements of identical cells and identical batteries.
(a) If the ammeter reading in circuit 02 is 0.3A, in which
circuit will the ammeter reading be 0.6A?
(b) If the ammeter reading in circuit 02 is 0.3A, in which circuit will the ammeter reading be 0.15A?
(c) If the ammeter reading in circuit 02 is 0.3A, in which
circuit will the ammeter reading be 0.9A
(d) If the ammeter reading in circuit 02 is 0.3A, in which circuit will the ammeter reading be 0.1A?
ANSWERS
INDEX of notes on drawing and interpreting
simple electrical circuits
2.4 (Set B) More complex bulb circuits
and deducing the current flow at various points in the circuit
Q5.
Circuit 18 shows how three lamps and four ammeters are wired together. The lamps are
NOT identical but all four switches are closed.
If ammeter a4 reads 8A, a1 reads 3A and a2 reads 2A,
what will be the current reading on ammeter a3?
ANSWERS
Q6.
Circuit 18 shows how three lamps and four ammeters are wired together. The lamps are
NOT identical but all four switches are closed.
If ammeter a1 reads 2A, a2 reads 1A and a3 reads 4A,
what will be the current reading on ammeter a4?
ANSWERS
Q7.
Circuit 20 shows a circuit arrangement for five switches (s) and six bulbs (b).
(a) Which bulbs light up if switch s5 is closed?
(b) Which bulbs light up if switches s1, s3 and s5 are closed?
(c) Which bulbs light up if switches s1, s2 and s5 are closed?
(d) Which bulbs light up if switches s1, s2, s4 and s5 are closed?
(e) Which bulbs light up if switches s1, s3, s4 and s5 are closed?
ANSWERS
Q8.
Circuit 21 shows the arrangement of six identical bulbs (X) and four ammeters (a1 to a4). To solve the problem you need to realise that each bulb has an identical resistance. The more bulbs there are in series, the greater the resistance to current flow.
(a) If a1 reads 3A and a4 reads 5.5A what will ammeter a2 read?
(b) If a1 reads 6A and a2 reads 3A what will ammeter a4 read?
(c) If a2 reads 4.5A and a3 reads 3.0A what will ammeter a1 read?
ANSWERS
Q9.
The Circuit 23 shows a two way switch s1 and a simple switch s2, connected to a power supply and five lamps (b1 to b5
(a) Which lamps will be ON when only switch s1a is closed?
(b) Which lamps will be ON when only switch s1b is closed?
(c) Which lamps will be ON when switches s1a and s2 are closed?
(d) Which lamps will be ON when switches s1b and s2 are closed?
Q10.
In the circuit 20 shown above, all the bulbs light up when all the switches are closed.
(a) What happens to the other bulbs if
bulb b2
'blows'?
(b) What happens to the other bulbs if
bulb b3
'blows'?
(c) What happens to the other bulbs if
bulb b4
'blows'?
(d) What happens to the other bulbs if
bulb b5
'blows?
(e) What happens to the other bulbs if
bulb b6
'blows'?
ANSWERS
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Key points abbot electric circuits in physics courses -
Information
sources for Doc Brown's key points: IGCSE-GCSE physics are based on textbooks
& syllabus-specifications for students taking the UK AQA,
Edexcel, OCR 21st Century Science, OCR Gateway science suite, WJEC, CCEA and
CIE GCSE
physics 9-1 level science examinations.
Keywords, phrases and learning objectives for
simple electrical circuits
Know how to solve simple problem solving by directly comparing simple circuit
diagrams/
In simple circuits, be able to deduce which bulbs
light up and lamps glow more or less brightly by comparing two or
more circuit diagrams of lamps.
Be able to deduce which bulbs light up and what
relative current might flow in more complex bulb (lamp circuits)
e.g. be able to deduce the current
flowing at various points in the circuit
Practice questions problem
solving with both series circuits and parallel circuits
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ANSWERS TO set A CIRCUIT DIAGRAM PROBLEMS
Q1.
From the four circuits shown:
(a) In which two circuits will the bulb/bulbs be the same brightness?
Answer: Circuits 01 and 05, same ratio of cells
to lamps (same resistance/lamp ratio)
(b) In which circuit/circuits will the lamps glow
the dimmest?
Answer: Circuit 04, the highest lamp/cell ratio,
more lamps in series, bigger resistance to current flow.
(c) In which circuit/circuits will the lamps glow
the brightest?
Answer: Circuit 07, highest cell/lamp ratio
(highest p.d./resistance ratio), in fact highly likely to blow
the bulb.
Q2.
From the four circuits shown
(a) Which two circuits will have the same
brightness?
Answer: Circuits 03 and 16, same cell/lamp ratio
(same p.d./resistance ratio).
(a) Which circuit will have the brightest lit lamp or lamps'?
Answer: Circuit 07, the highest cell/lamp ratio
(highest p.d./resistance ratio).
(c) Which circuit will have 'the dimmest lit
lamp/lamps?
Answer: Circuit 09, the lowest cell/lamp ratio
(lowest p.d./resistance ratio).
Q3.
From the four circuits shown:
(a) In which two 'will the lamps be the same brightness'?
Answer: 04 and 17, same cell/lamp ratio (same
p.d./resistance ratio)
(b) Which circuit/circuits will have the brightest
lit lamp/lamps?
Answer: Circuit 06, highest cell/lamp ratio (highest
p.d./resistance ratio).
(c) Which circuit will have the dimmest lamp/lamps?
Answer: Circuit 08, the lowest cell/lamp ratio
(lowest p.d./resistance ratio)
Q4.
The five circuits show various arrangements of identical cells and identical batteries.
(a) If the ammeter reading in circuit 02 is 0.3A, in which
circuit will the ammeter reading be 0.6A?
Answer:
Circuit 03,
same p.d., but 1 bulb, half the resistance of circuit 02
(b) If the ammeter reading in circuit 02 is 0.3A, in which circuit will the ammeter reading be 0.15A?
Answer:
Circuit 04,
same resistance of 2 lamps, but half the p.d. of circuit 02
(c) If the ammeter reading in circuit 02 is 0.3A, in which
circuit will the ammeter reading be 0.9A
Answer:
Circuit 07,
1.5 x p.d and half the resistance, so current 3x that of circuit
02.
(d) If the ammeter reading in circuit 02 is 0.3A, in which circuit will the ammeter reading be 0.1A?
Answer:
Circuit 08,
half the p.d. and 1.5 x the resistance of circuit 02, 1/3
current flow
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ANSWERS TO set B BULB CIRCUIT QUESTIONS
Q5.
Circuit 18 shows how three lamps and four ammeters are wired together. The lamps are
NOT identical but all four switches are closed. If ammeter a4 reads 8A, a1 reads 3A and a2 reads 2A,
what will be the current reading on ammeter a3?
Answer: Readings a4 = a1 + a2 + a3, therefore a3 =
a4 - a1 - a2 = 8 -3 -2 =
3A
Q6.
Circuit 18 shows how three lamps and four ammeters are wired together. The lamps are
NOT identical but all four switches are closed. If ammeter a1 reads 2A, a2 reads 1A and a3 reads 4A,
what will be the current reading on ammeter a4?
Answer: Readings a4 = a1 + a2 + a3 = 2 + 1 + 4
= 7A
Q7.
Circuit 20 shows a circuit arrangement for five switches (s) and six bulbs (b).
(a) Which bulbs light up if switch s5 is closed?
Answer
b1 only
(b) Which bulbs light up if switches s1, s3 and s5 are closed?
Answer:
b1, b2, b3 and b6
(c) Which bulbs light up if switches s1, s2 and s5 are closed?
Answer:
b1, b2, b4 and b5
(d) Which bulbs light up if switches s1, s2, s4 and s5 are closed?
Answer:
b1, b2, b4, b5 and b6
(e) Which bulbs light up if switches s1, s3, s4 and s5 are closed?
Answer:
b1, b2, b3, b5 and b6
Q8.
Circuit 21 shows the arrangement of six identical bulbs (X) and four ammeters (a1 to a4). To solve the problem you need to realise that each bulb has an identical resistance. The more bulbs there are in series, the greater the resistance to current flow.
(a) If a1 reads 3A and a4 reads 5.5A what will ammeter a2 read?
Answer: The ratio of the resistances is 1 : 2 :
3
The ratio of the current will be 3 : 2 : 1
a2 will be 1/2 of a1 due to double the
resistance, so
a2
will read 1.5A
(a3 will be 1/3 of a1 due to triple resistance)
(b) If a1 reads 6A and a2 reads 3A what will ammeter a4 read?
Answer: The ratio of the resistances is 1 : 2 :
3
The ratio of the current will be 3 : 2 : 1
a3 will read 1/3 of a1 = 2A (triple the
resistance, 1/3 of the current)
a4 = a1 + a2 + a3 = 6 + 3 + 2 =
11A
(c) If a2 reads 4.5A and a3 reads 3.0A what will ammeter a1 read?
Answer: The ratio of the resistances is 1 : 2 :
3
The ratio of the current will be 3 : 2 : 1
a2 will be 1/2 a1, so a1 reading =
9.0 A
Q9.
The Circuit 23 shows a two way switch s1 and a simple switch s2, connected to a power supply and five lamps (b1 to b5
(a) Which lamps will be ON when only switch s1a is closed?
Answer:
b2 and b3
(b) Which lamps will be ON when only switch s1b is closed?
Answer:
b1 and b4
(c) Which lamps will be ON when switches s1a and s2 are closed?
Answer:
b1, b2, b3 and b5
(d) Which lamps will be ON when switches s1b and s2 are closed?
Answer:
b1, b2, b4 and b5
Q10.
In the circuit 20 shown above, all the bulbs light up when all the switches are closed.
(a) What happens to the other bulbs if
bulb b2
'blows'?
Answer:
b1 still lit, b3, b4, b5
and b6 go out
(b) What happens to the other bulbs if
bulb b3
'blows'?
Answer:
b6 goes out, b1, b2, b4 and b5 stay lit
(c) What happens to the other bulbs if
bulb b4
'blows'?
Answer:
b5
goes out, b1, b2, b3 and b6 stay lit
(d) What happens to the other bulbs if
bulb b5
'blows?
Answer:
b4 goes out, b1, b2, b3
and b6 stay lit
(e) What happens to the other bulbs if
bulb b6
'blows'?
Answer:
b3
goes out, b1, b2, b4 and b5 stay lit
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Based on the syllabus-specifications
for students taking the IGCSE/GCSE level physics examinations summary
revision notes and key points on questions on problem solving by
comparing electrical circuits, worked out answers to problems, what
is current flow? which bulbs light up? for students taking the AQA
igcse/gcse physics notes on questions on problem solving by comparing electrical
circuits, what is current flow? which bulbs light up?, Edexcel gcse
physics notes on questions on problem solving by comparing
electrical circuits, what is current flow? which bulbs light up?, worked
out answers to problems OCR 21st century GCSE
physics notes on questions on problem solving by comparing
electrical circuits, what is current flow? which bulbs light up?, OCR gateway
GCSE physics notes on questions on problem solving by comparing
electrical circuits, what is current flow? which bulbs light up?,
worked out answers to problems WJEC gcse physics notes on questions
on problem solving by comparing electrical circuits, what is current
flow? which bulbs light up?, CCEA
gcse physics notes on questions on problem solving by comparing
electrical circuits, what is current flow? which bulbs light up? for students taking CIE Cambridge igcse
physics, worked out answers to problems or any other GCSE or IGCSE level physics exams notes on
questions on problem solving by comparing electrical circuits, what
is current flow? which bulbs light up?, useful for US grade 9-10 physics courses
INDEX for notes on
drawing and interpreting simple electrical circuits
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