Year 9 Science · Unit 3 · Lesson 19

Ohm's Law

Foundation Worksheet

Name

Date

Class

Learning Goals

Use V = IR and its rearrangements to find a missing quantity.
Describe how to connect the meters to test whether a resistor is ohmic.
Use a V–I graph to find a resistance and tell ohmic from non-ohmic conductors.

Warm Up

Match each form of Ohm’s law to what it calculates

Write the letter in the middle column. Each letter is used once.

Formula	Letter	What it calculates
V = I × R		A. The current, in amps, when you know the voltage and the resistance
I = V ÷ R		B. The resistance, in ohms, when you know the voltage and the current
R = V ÷ I		C. The voltage, in volts, when you know the current and the resistance

1. Complete the table for the three quantities in Ohm’s law.

Recall 2 marks

Quantity	Letter in V = I × R	Unit, and its symbol
Voltage
Current
Resistance

Your Turn

2. Use Ohm’s law to find the missing value in each row. Show your working.

Apply 4 marks

Voltage (V)	Current (A)	Resistance (Ω)
12		4
6	2
	3	10
9		45

True or false? Fix the false ones

Circle T or F. If a statement is false, correct it on the line.

V = IR means that voltage equals current multiplied by resistance.

Correct it:

For the same voltage, increasing the resistance increases the current.

Correct it:

A light bulb filament is an ohmic conductor.

Correct it:

For an ohmic resistor, doubling the voltage doubles the current.

Correct it:

Fill the gap: testing a resistor

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

series parallel voltage current origin ohmic non-ohmic gradient temperature

To test a resistor, connect the ammeter in with the resistor, and the voltmeter in across it. Use a variable power supply to change the , and record the at each setting. Plot voltage (vertical axis) against current (horizontal axis). If the points lie on a straight line through the , the resistor is , and the of the line is equal to its resistance.

Go Deeper

Investigation: testing a resistor

Ella’s group used this method on one resistor and recorded Table 1.

Table 1. Voltage and current for the resistor

Voltage (V)	Current (A)
0	0
1.5	0.10
3.0	0.20
4.5	0.30
6.0	0.40

Source: sample class results.

3. Plot voltage (vertical axis) against current (horizontal axis), and draw a line of best fit.

Apply 3 marks

Graph 1. Title: ______________________________

4. (a) Pick one pair of readings and work out R = V ÷ I. (b) What current would flow at 9.0 V?

Apply 3 marks

(a) Resistance Ω

(b) Current at 9.0 V A

5. Is this resistor ohmic? Give two pieces of evidence from your graph or from Table 1.

Analyse 2 marks

Show What You Know

6. Compare the resistor in Table 1 with the filament of a torch bulb. Describe the V–I graph of each one, and explain, using temperature, why the filament’s resistance changes as the current rises but the resistor’s does not.

Apply 5 marks