Physics · Class 12

Active learning ideas

Ohm's Law and Resistance

Active learning works best for Ohm's Law because students often struggle with abstract proportional relationships without concrete evidence. When they measure voltage, current, and resistance themselves, the mathematical model becomes meaningful. Labs and group work transform resistance from a formula into a physical property they can observe and manipulate.

• CBSE Learning Outcomes
• CBSE: Current Electricity - Class 12

• 30–45 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Problem-Based Learning
• 40 min · Pairs

Pairs Lab: Verifying Ohm's Law

Pairs connect a fixed resistor, variable power supply, ammeter, and voltmeter in series. They vary voltage from 2V to 10V in steps, record current, plot V-I graph, and calculate resistance from slope. Discuss if the graph is linear.

Predict how the current in a circuit changes if the voltage is doubled while resistance remains constant.

Facilitation Tip

During the Pairs Lab, remind students to record at least five data points for each resistor to ensure accurate V-I graphs.

What to look for

Present students with a circuit diagram containing a known voltage source and resistance. Ask them to calculate the current using Ohm's Law. Then, ask them to predict what would happen to the current if the voltage were doubled, and to explain their reasoning.

• Analyze
• Evaluate
• Create
• Decision-Making
• Self-Management
• Relationship Skills

Activity 02

• Problem-Based Learning
• 45 min · Small Groups

Small Groups: Factors Affecting Resistance

Groups measure resistance of wires varying length, thickness, and material using a metre bridge or multimeter. They tabulate data, graph resistance versus length or area, and derive formulas. Compare results across groups.

Compare ohmic and non-ohmic conductors, providing examples of each.

Facilitation Tip

For the Small Groups activity on resistance factors, provide rulers and micrometers so students measure length and diameter precisely.

What to look for

Provide students with a V-I graph showing a linear relationship and another showing a non-linear relationship. Ask them to identify which graph represents an ohmic conductor and which represents a non-ohmic conductor, and to justify their choices.

• Analyze
• Evaluate
• Create
• Decision-Making
• Self-Management
• Relationship Skills

Activity 03

• Problem-Based Learning
• 30 min · Whole Class

Whole Class Demo: Ohmic vs Non-Ohmic

Demonstrate linear graph for resistor and curved for filament lamp using data projector. Class notes differences, predicts behaviour for new voltages. Follow with pair predictions on given graphs.

Evaluate the impact of temperature on the resistance of different materials.

Facilitation Tip

In the Whole Class Demo, use identical bulbs and diodes side-by-side so students compare slopes directly on the same axes.

What to look for

Pose the question: 'How does the temperature of a metal wire affect its resistance, and why is this different for a semiconductor like silicon?' Facilitate a class discussion where students explain the microscopic reasons behind these observations.

• Analyze
• Evaluate
• Create
• Decision-Making
• Self-Management
• Relationship Skills

Activity 04

• Problem-Based Learning
• 35 min · Small Groups

Small Groups: Temperature Effect

Groups immerse wires or thermistors in hot water, measure resistance before and after using multimeter. Plot resistance versus temperature, classify materials. Discuss real applications like fuses.

Predict how the current in a circuit changes if the voltage is doubled while resistance remains constant.

Facilitation Tip

During the Small Groups activity on temperature effects, instruct students to heat wires slowly and measure resistance at 10°C intervals to see the trend clearly.

What to look for

Present students with a circuit diagram containing a known voltage source and resistance. Ask them to calculate the current using Ohm's Law. Then, ask them to predict what would happen to the current if the voltage were doubled, and to explain their reasoning.

• Analyze
• Evaluate
• Create
• Decision-Making
• Self-Management
• Relationship Skills

A few notes on teaching this unit

Teachers should begin with simple circuits where students build confidence before introducing complex variables like temperature. Avoid rushing to the formula; let students derive Ohm's Law from their own data first. Use everyday materials like nichrome wires and LEDs to make concepts relatable, and always connect mathematical results back to physical changes in the circuit.

By the end of these activities, students will confidently define resistance, calculate unknowns using V = IR, and distinguish ohmic from non-ohmic conductors through experimental data. They will also explain why temperature and dimensions change resistance, linking microscopic behavior to macroscopic measurements.

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Watch Out for These Misconceptions

• During the Pairs Lab on verifying Ohm's Law, watch for students assuming all conductors follow Ohm's Law equally.

  Have students graph data for both a metal wire and a filament bulb, then ask them to compare the linearity of both graphs. Prompt them to explain why the bulb’s curve bends, linking this to temperature changes in non-ohmic conductors.

• During the Small Groups activity on factors affecting resistance, watch for students predicting resistance decreases with longer wires.

  Provide a multimeter and wires of different lengths cut to identical diameters. Ask students to measure resistance for each length and plot the results, then discuss why the graph shows a rising line instead of a falling one.

• During any circuit-building activity, watch for students believing current exists without voltage.

  In the Pairs Lab, have students build a circuit with zero voltage and measure the current. Ask them to explain why the current is zero, reinforcing that voltage is the driving force behind current flow as per Ohm's Law.

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Methods used in this brief

• Problem-Based Learning