Year 9 Science · Unit 3 · Lesson 20

Checkpoint 3, Circuits, Series, Parallel & Ohm's Law

Foundation Worksheet

Name

Date

Class

Learning Goals

Recall the key words and rules for circuits from Lessons 17 to 19.
Use meter readings and Ohm’s law to find unknown resistances in a series circuit.
Explain why a string of lamps wired in series goes dark when one lamp fails.

Warm Up

Fill the gap

Choose the correct word from the word bank. Each word is used once. Two words will not be used.

voltage current parallel watts Ohm’s law circuit resistance series amperes

Australian homes use wiring, so every appliance is connected across the same two supply wires. Each appliance receives the full mains of 230 V, no matter what else is switched on. The flow of charge around a is called , and it is measured in (A). The rule that links voltage, current and is called : V = I × R.

1. What does an ammeter measure, and in what unit? What does a voltmeter measure, and in what unit?

Recall 2 marks

Your Turn

Sort it: series, parallel or Ohm’s law?

Write each statement in the correct column. Each column gets four statements.

V = I × R There is only one path for the current Every branch has the full supply voltage A single faulty lamp turns every lamp off R = V ÷ I The branch currents add up to the current from the supply The lamps share the battery’s voltage Doubling the voltage doubles the current through an ohmic resistor How the power points in a house are wired Two ammeters anywhere in the loop give the same reading A lamp can be removed and the others stay lit A straight-line V–I graph through the origin

Series circuit

Parallel circuit

Ohm’s law

2. A student connects a 12 V battery to a 6 Ω resistor. Use Ohm’s law to calculate the current. Show the formula and your working.

Apply 2 marks

Current A

Go Deeper

Investigation: meter readings in a series circuit

Table 1 lists the meters Ruby placed around a loop of two resistors, R₁ and R₂, and a 12.0 V battery. Two readings were not written down.

Table 1. Meter readings

Meter	Where it is connected	Reading
A₁	Between the battery and R₁	0.50 A
A₂	Between R₁ and R₂
V₁	Across R₁	4.0 V
V₂	Across R₂
V₃	Across the battery	12.0 V

Source: sample class results.

3. Fill in the two missing readings, and name the series rule you used for each one.

Apply 2 marks

4. Work out R₁ and R₂ with R = V ÷ I, then add them to find the total resistance.

Apply 3 marks

R₁ Ω

R₂ Ω

Total resistance Ω

5. Show that dividing 12.0 V by the ammeter reading gives the same total. Why does R₂ take the bigger share of the 12.0 V?

Analyse 2 marks

Show What You Know

Scenario: party lights on a verandah

A string of 20 small lamps is wired in series and plugged into a low-voltage power supply. One evening the whole string goes dark, although the power supply is still working.

6. Explain why the whole string went dark, and describe how you could find the faulty lamp. Then explain whether wiring the lamps in parallel would be better, giving one advantage and one disadvantage.

Apply 5 marks