Physics · Year 10 · Electricity and Circuits · Spring Term

I-V Characteristics of Components

Students will investigate and interpret the current-voltage characteristics of ohmic and non-ohmic components.

• National Curriculum Attainment Targets
• GCSE: Physics - Electricity

About This Topic

I-V characteristics reveal how current responds to voltage changes in circuit components. Ohmic components, such as fixed resistors, produce straight-line graphs through the origin, indicating constant resistance regardless of voltage. Non-ohmic components behave differently: filament lamps show increasing resistance as the wire heats up, curving the graph concave down; diodes conduct current primarily in forward bias above a threshold voltage, with negligible reverse flow.

Students build simple circuits with ammeters, voltmeters, and components to collect data points, then plot and interpret graphs. This meets GCSE Physics Electricity standards, directly tackling differentiation of ohmic and non-ohmic behaviour, explanation of lamp temperature effects, and diode current prediction. Graph analysis sharpens data skills and circuit prediction abilities essential for advanced topics like power dissipation.

Active learning suits this topic perfectly. Hands-on measurements let students see real-time current changes, while collaborative graphing and peer comparison of curves correct intuitive errors about linear behaviour. Predicting outcomes before testing fosters scientific reasoning and makes abstract relationships concrete.

Key Questions

1. Differentiate between ohmic and non-ohmic components based on their I-V graphs.
2. Explain why the resistance of a filament lamp increases with temperature.
3. Predict the current through a diode given its forward bias voltage.

Learning Objectives

• Compare the I-V characteristics of ohmic and non-ohmic components by analyzing plotted data.
• Explain the relationship between temperature and resistance in a filament lamp using its I-V graph.
• Calculate the resistance of an ohmic component at different voltage points from its I-V characteristic.
• Classify components as ohmic or non-ohmic based on their I-V characteristic curves.
• Predict the current flow through a diode at a given forward bias voltage from its I-V graph.

Before You Start

Electric Current and Voltage

Why: Students need a foundational understanding of what electric current and voltage represent to investigate their relationship.

Basic Circuit Components

Why: Familiarity with components like resistors, ammeters, and voltmeters is necessary for building the experimental circuits.

Calculating Resistance

Why: Students should be able to use Ohm's Law (R=V/I) to calculate resistance before investigating how it changes.

Key Vocabulary

Ohmic component	A component whose resistance remains constant regardless of the voltage applied across it. Its I-V graph is a straight line passing through the origin.
Non-ohmic component	A component whose resistance changes with the applied voltage or current. Its I-V graph is not a straight line.
Resistance	The opposition to the flow of electric current. It is calculated as voltage divided by current (R = V/I).
Filament lamp	A component that produces light when an electric current passes through a thin wire (filament), causing it to heat up and glow.
Diode	A semiconductor device that primarily conducts current in one direction (forward bias) and blocks it in the opposite direction (reverse bias).

Watch Out for These Misconceptions

Common Misconception

All components have constant resistance like resistors.

What to Teach Instead

Students often assume linear I-V for everything. Building circuits with lamps reveals curving graphs; group plotting and overlaying data helps visualise non-linearity, shifting mental models through evidence.

Common Misconception

Diodes conduct equally in both directions.

What to Teach Instead

Reverse bias confusion persists. Testing forward and reverse in pairs, then peer-teaching results, clarifies one-way flow. Discussion of real graphs reinforces threshold effects over memorisation.

Common Misconception

Filament lamp resistance decreases when hot.

What to Teach Instead

Intuition from brighter light suggests lower resistance. Measuring sequential I-V runs as lamp heats, with class data pooling, shows increasing slope; active prediction-testing cycles build accurate understanding.

Active Learning Ideas

Circuit Building: Resistor I-V Graph

Pairs connect a resistor, ammeter, and variable power supply in series with a voltmeter across the resistor. They record I and V for voltages from 0-6V in 1V steps, plot the graph, and calculate resistance from gradient. Discuss why the line is straight.

30 min·Pairs

Stations Rotation: Component Characteristics

Set up stations for resistor, lamp, and diode. Small groups measure I-V data at each for 10 minutes, swap components, then combine class data to plot shared graphs. Compare shapes and predict resistance changes.

50 min·Small Groups

Prediction Challenge: Diode Forward Bias

Individuals sketch expected I-V for a diode from description, then test in circuit with 0.2V steps from 0-1V. Groups share predictions vs results, explaining threshold voltage. Extend to reverse bias.

40 min·Individual

Graph Matching Relay

Whole class divides into teams. Teams match printed I-V graphs to components (resistor, lamp, diode) and justify in relay format: one student runs to board per correct match. Debrief curves.

20 min·Whole Class

Real-World Connections

• Electrical engineers designing lighting systems for concert venues must understand the non-ohmic behavior of filament lamps to manage heat and ensure consistent brightness.
• Technicians repairing electronic devices use I-V characteristic curves to diagnose faulty components like diodes in circuit boards, ensuring proper signal flow.
• Manufacturers of LEDs use precise control of forward bias voltage to achieve specific light outputs, demonstrating the predictable non-ohmic behavior of semiconductor junctions.

Assessment Ideas

Quick Check

Provide students with three different I-V graphs, each representing an ohmic resistor, a filament lamp, and a diode. Ask them to label each graph and write one sentence justifying their classification for each component.

Discussion Prompt

Pose the question: 'Why does the resistance of a filament lamp increase as it gets hotter?' Encourage students to refer to their experimental data and the shape of the I-V graph to explain the physical reason behind this change.

Exit Ticket

Give students a partial I-V graph for a diode. Ask them to extend the graph to show typical behavior in forward bias and reverse bias, and then predict the approximate current if the voltage is increased by 0.5V in the forward bias region.

Frequently Asked Questions

How do I differentiate ohmic and non-ohmic components for Year 10?

Use I-V graphs: straight line through origin means ohmic (constant R = gradient). Curved graphs indicate non-ohmic, like lamps (R increases with temperature) or diodes (forward conduction only). Hands-on circuit work with plotting reinforces this; students calculate R at multiple points to see changes clearly.

Why does filament lamp resistance increase with temperature?

As current flows, the tungsten filament heats, causing atoms to vibrate more and impede electron flow, raising resistance. This curves the I-V graph concave down. Students confirm by measuring hotter runs after cool-down, linking to atomic structure and real-world bulb limits.

How can active learning help students understand I-V characteristics?

Circuit-building activities make graphs tangible: students measure live data, plot curves, and predict diode thresholds before testing. Small-group stations rotate components for broad exposure; peer data sharing reveals patterns like lamp heating effects. This beats lectures by building intuition through trial, error, and collaboration, boosting retention and graphing skills.

What practical setup works best for diode I-V graphs?

Series circuit: power supply, diode, ammeter, voltmeter across diode. Use low voltages (0-2V forward, -1V reverse) to avoid damage. Students tabulate 0.1V steps, plot, and note 0.6V knee. Safety: supervise polarity; extend to LED variants for colour threshold comparison.