Physics · Year 10 · Electricity and Circuits · Spring Term

Resistance and Ohm's Law

Students will define resistance and apply Ohm's Law to calculate current, voltage, or resistance.

• National Curriculum Attainment Targets
• GCSE: Physics - Electricity

About This Topic

Resistance measures how much a component opposes electric current, quantified in ohms. Ohm's Law states that voltage equals current multiplied by resistance (V = I × R), allowing students to calculate any one variable if the other two are known. At GCSE level, students apply this to simple circuits and explore how resistance in wires increases with length, decreases with cross-sectional area, and varies by material.

This topic sits within the Electricity unit, linking to series and parallel circuits studied earlier. Students develop skills in data analysis by plotting voltage-current graphs, which should be straight lines through the origin for ohmic conductors. Practical work verifies the law and factors affecting resistance, fostering experimental design and evaluation.

Active learning suits this topic well. When students build circuits, measure values with ammeters and voltmeters, and graph results in small groups, they see direct relationships emerge from data. This hands-on approach corrects misconceptions through real evidence and builds confidence in quantitative problem-solving.

Key Questions

1. Analyze the relationship between current, voltage, and resistance as described by Ohm's Law.
2. Evaluate how the resistance of a wire changes with its length, cross-sectional area, and material.
3. Design an experiment to verify Ohm's Law for a resistor.

Learning Objectives

• Calculate the current, voltage, or resistance in a simple circuit using Ohm's Law.
• Analyze the graphical relationship between voltage and current for an ohmic conductor.
• Evaluate how the length, cross-sectional area, and material of a wire affect its resistance.
• Design an experiment to investigate the factors influencing the resistance of a wire.

Before You Start

Electric Current and Voltage

Why: Students must understand the fundamental concepts of electric current and voltage before they can explore how resistance affects them.

Basic Circuit Components

Why: Familiarity with components like resistors, wires, ammeters, and voltmeters is necessary for understanding and applying Ohm's Law in practical contexts.

Key Vocabulary

Resistance	A measure of how difficult it is for an electric current to flow through a component. It is measured in ohms (Ω).
Ohm's Law	A fundamental law stating that the voltage across a conductor is directly proportional to the current flowing through it, provided all physical conditions and temperature remain constant. Mathematically, V = I × R.
Voltage	The electric potential difference between two points in a circuit, measured in volts (V). It is the 'push' that drives current.
Current	The rate of flow of electric charge, measured in amperes (A).
Ohmic Conductor	A component or device that obeys Ohm's Law, meaning its resistance remains constant regardless of the voltage applied or current flowing through it.

Watch Out for These Misconceptions

Common Misconception

Resistance works like friction slowing water in a pipe.

What to Teach Instead

Resistance arises from collisions between electrons and atoms in conductors. Hands-on circuit building shows current drops with higher resistance at fixed voltage, helping students visualise electron flow rather than mechanical analogy through direct measurements.

Common Misconception

Ohm's Law applies to all components equally.

What to Teach Instead

It holds only for ohmic conductors like metal wires; lamps and diodes are non-ohmic. Graphing activities reveal non-linear V-I curves for these, where group discussions refine understanding via evidence comparison.

Common Misconception

Thicker wires have higher resistance.

What to Teach Instead

Resistance decreases with larger cross-sectional area as electrons have more paths. Wire investigation stations let students test multiples, observe inverse trends, and correct ideas through plotted data.

Active Learning Ideas

Circuit Stations: Ohm's Law Verification

Prepare stations with resistors, power supplies, ammeters, and voltmeters. Students at each station measure current and voltage for three resistors, record data, then plot V-I graphs. Groups swap stations to compare results and identify ohmic behaviour.

45 min·Small Groups

Pairs Investigation: Wire Resistance Factors

Provide wires of different lengths, thicknesses, and materials. Pairs connect each to a circuit, measure resistance using a multimeter, and tabulate results. They predict trends before testing and discuss patterns in resistance changes.

30 min·Pairs

Whole Class: Design Your Experiment

Pose the challenge to verify Ohm's Law. Students brainstorm variables, sketch circuits, and vote on the best design. Implement the class-chosen method, collect shared data, and analyse as a group.

50 min·Whole Class

Individual: Calculation Challenges

Distribute worksheets with circuit diagrams and given values. Students calculate missing V, I, or R values, then check by simulating on circuit software. Peer review follows to explain workings.

20 min·Individual

Real-World Connections

• Electrical engineers designing power grids must account for the resistance of transmission lines to minimize energy loss as heat, ensuring efficient delivery of electricity to homes and businesses.
• Manufacturers of electronic devices, such as smartphones and laptops, select specific materials and wire gauges for internal components to manage heat dissipation and ensure reliable performance, directly applying principles of resistance.
• Appliance designers consider the resistance of heating elements in devices like toasters and kettles. By controlling the resistance, they can regulate the amount of heat produced for cooking or boiling water.

Assessment Ideas

Quick Check

Present students with three circuit scenarios, each providing two values (e.g., voltage and resistance) and asking them to calculate the missing third value (current). For example: 'A circuit has a voltage of 12V and a resistance of 4Ω. Calculate the current.'

Discussion Prompt

Ask students: 'Imagine you have two wires of the same material, one twice as long as the other. How would their resistances compare? Justify your answer using your understanding of resistance.' Facilitate a class discussion to compare their reasoning.

Exit Ticket

Provide students with a simple V-I graph for an ohmic conductor. Ask them to: 1. State the resistance of the conductor based on the graph. 2. Predict the voltage if the current were 3A. 3. Explain why the graph is a straight line through the origin.

Frequently Asked Questions

How do you teach factors affecting wire resistance?

Start with predictions based on particle model: longer paths mean more collisions, wider paths offer more routes. Use multimeters on varied wires for direct measurement, then graph length vs resistance. Class data pooling shows clear proportional relationships, reinforcing quantitative links.

What experiments verify Ohm's Law in Year 10?

Build series circuits with fixed resistors, vary voltage, and measure current. Plot graphs; straight lines confirm V = I R. Control variables like temperature, repeat for reliability. Students evaluate anomalies, linking to GCSE practical skills.

How can active learning help students master Ohm's Law?

Circuit-building tasks with real components let students manipulate variables and see instant feedback from meters. Small group graphing turns raw data into linear proofs, while peer teaching during station rotations clarifies calculations. This beats passive notes, as tangible results build lasting proportional reasoning.

Why plot voltage against current graphs?

Graphs reveal ohmic linearity: gradient equals resistance. Non-straight lines flag non-ohmic behaviour. Students practise interpolation, extrapolation, and error analysis, key for GCSE exams. Digital tools like data loggers speed collection for more points and precision.