Complex bulb lamp circuits and deducing the current flow at various points in the circuit practice questions problem solving series circuits parallel circuits IGCSE/GCSE Physics revision notes

Electrical circuits: 2.5 More complex bulb circuits: Deducing the current flow at various points in the circuit

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INDEX for physics notes on drawing and interpreting simple electrical circuits

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ANSWERS to ALL the QUESTIONS at the end of the page

2.5 More complex bulb circuits and deducing the current flow at various points in the circuit

Q1.

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

Q2.

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

Q3.

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

Q4.

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

Q5.

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?

Q6.

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

Keywords, phrases and learning objectives for more complex electrical circuits

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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INDEX for notes on drawing and interpreting simple electrical circuits

ANSWERS TO BULB CIRCUIT QUESTIONS

Q1.

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

Q2.

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

Q3.

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

Q4.

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

Q5.

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

Q6.

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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