Year 9 Science · Unit 3 · Lesson 18

Series and Parallel Circuits

Foundation Worksheet

Name

Date

Class

Learning Goals

Sort features of circuits into series, parallel or both.
Use the rules for series and parallel circuits to fill in missing meter readings.
Explain why Australian homes are wired in parallel.

Warm Up

Sort it: series, parallel or both?

Write each statement in the correct box.

Joined end to end in one loop Full battery voltage on each branch Needs a complete path for current Same current through every part Power points in Australian homes One lamp fails, so all go out Branch currents add up to the total Ammeter goes in series with what it measures Old-style Christmas lights One branch fails, the others keep working Another lamp dims every lamp

Series circuit

Parallel circuit

Both

Your Turn

1. Explain why old-style Christmas lights, wired in series, all went out when one bulb failed, but the lights in a house stay on when one globe blows.

Recall 2 marks

Match each feature to its rule

Write the letter of the matching rule from the bank, then give a short reason. Each letter is used once.

A. Other branches keep working B. Wiring in Australian homes: each appliance gets the full mains voltage C. The voltage is shared among the components D. Each appliance can be switched on or off by itself E. The current is the same at every point F. Add the resistances: total R = R₁ + R₂ + R₃

Circuit feature	Letter	Reason (why?)
Voltage in a series circuit
Current in a series circuit
One component fails in a parallel circuit
Total resistance in a series circuit
A common use of parallel circuits
Switches in a parallel circuit

2. Three identical lamps share a 9 V battery in one loop. (a) What voltage does each lamp get? (b) The lamps are rewired side by side, each one across the battery. What voltage does each lamp get now?

Apply 2 marks

(a) Series, each lamp V

(b) Parallel, each lamp V

Go Deeper

Investigation: two lamps, two circuits

Priya’s group put two identical lamps on a 6.0 V battery, first in series and then in parallel. Some of their meter readings were not written down.

Table 1. Meter readings for the two circuits

Reading	Series circuit	Parallel circuit
Current through lamp 1 (A)	0.25	0.40
Current through lamp 2 (A)		0.40
Current from the battery (A)
Voltage across lamp 1 (V)	3.0
Voltage across lamp 2 (V)

Source: sample class results.

3. Fill in the six missing readings in Table 1.

Apply 3 marks

4. Use P = V × I to compare the power of one lamp in each circuit. Which circuit had the brighter lamps, and why?

Analyse 3 marks

One lamp, series W

One lamp, parallel W

Show What You Know

5. Explain why the lights and power points in Australian homes are wired in parallel. Give two advantages of parallel wiring, and one problem that comes from switching on many appliances on the same circuit.

Apply 5 marks