Ohm's Law Lesson Plan with a Virtual Lab

This Ohm's law lesson plan uses a free virtual lab so every student can measure current, voltage and resistance in one class period, without a box of meters that read zero because of a loose lead. Students predict, collect data, plot current against voltage, find the resistance from the slope, then test what happens when the resistance changes. Everything is ready to use: learning goals, setup, prediction questions, a step-by-step activity with data tables and the values students should get, discussion questions with answers, a series and parallel extension, and ideas for differentiation. All numbers come from the simulation's own model.

Lesson at a glance

• Level: grades 8–10 (ages 13–16), physical science or introductory physics.
• Time: one 50–60 minute period, plus an optional 20-minute extension.
• Prior knowledge: current as a flow of charge, voltage as the push from a battery, ammeters and voltmeters, reading a graph.
• Format: pairs on laptops, tablets or phones, or the whole class with one projector.
• Simulation: Ohm's law – voltage, current and resistance. Extension: DC circuit construction kit.

Learning goals

By the end of the lesson, students can:

1. State that for a fixed resistor the current is directly proportional to the voltage.
2. State that for a fixed voltage the current is inversely proportional to the resistance.
3. Plot a current–voltage graph and find the resistance from its slope (slope = 1/R).
4. Use V = IR, rearranged as needed, and convert between amperes and milliamperes.
5. (Extension) Measure current and voltage in series and parallel circuits.

What the simulation does

The simulation shows a simple loop: a row of 1.5 V cells, a resistor and an ammeter. Two sliders set the voltage, 0.1–9.0 V in steps of 0.1 V, and the resistance, 10–1,000 Ω in steps of 1 Ω. The current is calculated as I = U/R and shown in milliamperes to one decimal place. The defaults are 4.5 V and 500 Ω, which give 9.0 mA.

A few details worth knowing before class:

• Notation. The simulation writes voltage as U, the symbol used in much of Europe. Most US textbooks write V = IR. Tell students they are the same quantity.
• Visual cues. The letters in U = I · R grow and shrink with their values, one cell appears for every 1.5 V (up to six cells), the resistor gets more "impurity dots" as R rises, and the charges move faster as the current grows.
• Record data. Record data adds the current U, R and I to a table and plots the point on a graph of I (mA) against U (V). The table holds 10 rows; the eleventh pushes out the oldest. Clear table empties it.
• Graph scale. The built-in graph runs from 0 to 1,000 mA, so currents of a few milliamperes sit on the axis. That is why this lesson uses small resistances of 10 to 200 Ω.

Materials and setup before class

Materials: one device per pair (or a projector), the data tables below on paper, graph paper or a spreadsheet, and a calculator.

Setup (10 minutes, once):

1. Open the simulation and set U = 1.5 V and R = 20 Ω.
2. Click Share and create a link for each class, for example "Science · Period 4". The link pins these starting values, so every student begins in the same place.
3. Optional: on the Questions tab, add the three predictions below as "Before, as a prediction", with Ask again after the simulation ticked. The simulation stays locked until each student commits. See the Predict–Observe–Explain guide for why this works.
4. Post the link, or open it in present mode and show the QR code.

Lesson sequence

1. Hook and predictions (8 minutes)

Project the simulation at the defaults and drag the voltage slider slowly up and down. Ask students what they notice about the moving charges and the letter I. Then have them commit to three predictions, on paper or on the link:

• P1. "The voltage across a resistor doubles from 3.0 V to 6.0 V. The current… halves / stays the same / doubles / quadruples."
• P2. "The voltage stays at 6.0 V and the resistor changes from 20 Ω to 60 Ω. The current… triples / stays the same / falls to one third / falls by 40 mA."
• P3. "Predict the current, in mA, for 9.0 V across 10 Ω."

Expect "falls by 40 mA" from students who think subtraction, and 0.9 for P3 from students who forget to convert to milliamperes. The answers are: doubles, falls to one third, and 900 mA.

2. Current and voltage: collect data (15 minutes)

Pairs keep R = 20 Ω and set U to each value in the table, pressing Record data each time. Then they change R to 50 Ω and repeat. That fills the simulation's table with exactly 10 rows. Students copy every reading into their own table, because the built-in table drops old rows. The last column is for you; leave it blank on the student copy.

R (Ω)	U (V)	Cells shown	I (mA)	Expected I (mA)
20	1.5	1		75.0
20	3.0	2		150.0
20	4.5	3		225.0
20	6.0	4		300.0
20	7.5	5		375.0
50	1.5	1		30.0
50	3.0	2		60.0
50	4.5	3		90.0
50	6.0	4		120.0
50	7.5	5		150.0

The simulation calculates I = U/R exactly, so readings should match to the last digit. If a pair's numbers are off, the slider is almost always one step away from the target value. On a computer, click a slider and use the arrow keys for single steps.

Ask pairs to write two patterns. Good answers: "When U doubles, I doubles" and "With 50 Ω the current is always 2.5 times smaller than with 20 Ω."

3. Graph current against voltage (10 minutes)

Students plot I (mA) on the vertical axis against U (V) on the horizontal axis, with both resistors on one graph. A 0–400 mA scale works well. The simulation's own graph shows the same points, squeezed into the bottom of a 0–1,000 mA axis.

Both sets of points form straight lines through the origin. Now find the slopes:

• 20 Ω: slope = 375.0 mA ÷ 7.5 V = 50 mA/V = 0.050 A/V. Then 1 ÷ 0.050 = 20 Ω.
• 50 Ω: slope = 150.0 mA ÷ 7.5 V = 20 mA/V = 0.020 A/V. Then 1 ÷ 0.020 = 50 Ω.

The key idea: the slope of an I–V graph is 1/R, so a steeper line means a smaller resistance. Students who convert the slope to A/V before inverting get the resistance back exactly. Students who forget the conversion get 0.02 or 0.05 Ω, a useful mistake to discuss.

4. Current and resistance (8 minutes)

Pairs press Clear table, set U = 6.0 V and record the current for each resistance. Expected values:

R (Ω)	10	20	30	60	100	200
I (mA)	600.0	300.0	200.0	100.0	60.0	30.0
I × R (V)	6.0	6.0	6.0	6.0	6.0	6.0

Have students add the last row themselves (converting mA to A first). The product is always 6.0 V: current and resistance are inversely proportional. Check P2: from 20 Ω to 60 Ω, the current falls from 300 mA to 100 mA, one third, not 40 mA less.

5. Exit check (5 minutes)

Three quick questions, on paper or as number questions on the link:

• "A circuit has 7.2 V across 40 Ω. What is the current?" Answer: 180 mA (accept ± 1).
• "A student measures 4.8 V and 160 mA. What is the resistance?" Answer: 30 Ω. Students can check it: 4.8 V and 30 Ω give 160.0 mA.
• "Which resistance gives 250 mA at 5.0 V?" Answer: 20 Ω.

The formative assessment guide shows how to set these up so they are checked automatically and compared across classes.

Discussion questions and answers

Use these with the whole class after step 4.

1. Why does the I–V graph pass through the origin? With no voltage there is no push, so there is no current. With the resistance fixed, the current is proportional to the voltage, and a proportional graph is a straight line through the origin.
2. What does a steeper line tell you? A smaller resistance. The slope is 1/R: the 20 Ω line climbs 50 mA per volt and the 50 Ω line only 20 mA per volt.
3. Set 3.0 V with 20 Ω, then 6.0 V with 40 Ω. What do you notice? Both give 150 mA. Doubling both U and R leaves the current unchanged, because I = U/R.
4. Is the current used up by the resistor? No. The current is the same all the way around a single loop. The resistor reduces the current everywhere in the loop, not only after it. The extension lets students test this with two ammeters.
5. What is the largest current this circuit can have? 9.0 V across 10 Ω gives 900 mA. A real 10 Ω resistor would get hot: it dissipates P = UI = 9.0 × 0.9 = 8.1 W.

Then return to the predictions. If you used the link, open View answers and show the Prediction and After columns side by side. Students like seeing how many minds changed, especially on P2.

Extension: series and parallel with the DC circuit kit

For a second lesson or fast finishers, move to the circuit construction kit. On its Intro screen, every battery is 9 V and every resistor and bulb is 10 Ω, so the numbers link directly to the Ohm's law simulation: 9.0 V across 10 Ω gave 900 mA there.

Students build each circuit from the box on the left, then tap a component to see its voltage and current, or drag the voltmeter and ammeter from the tray. To save building time, pin the "Two bulbs in series" or "Two bulbs in parallel" starting circuit on a link.

Circuit (9 V battery, 10 Ω each)	Current through battery	Current in each component	Voltage across each component
One resistor	900 mA	900 mA	9.00 V
Two in series	450 mA	450 mA	4.50 V
Two in parallel	1.80 A	900 mA	9.00 V

Questions to ask:

• "Two 10 Ω resistors in series behave like one resistor of what value?" 20 Ω: 9 V ÷ 0.45 A. Check it in the Ohm's law simulation: 9.0 V and 20 Ω give 450.0 mA.
• "Two in parallel behave like what?" 5 Ω: 9 V ÷ 1.8 A. That is below the Ohm's law simulation's 10 Ω minimum, a good reminder that adding a parallel branch lowers the total resistance.
• "Place the ammeter on the wire before the first resistor and after the second. What do you see?" The same 450 mA, which answers discussion question 4.

On the Lab screen, students can set values themselves. A 10 Ω and a 20 Ω resistor in series on 9 V give 300 mA, with 3.00 V and 6.00 V across them: the larger resistor takes the larger share of the voltage. The same two resistors in parallel draw 900 mA and 450 mA, 1.35 A in total.

Differentiation

Support:

• Give the data table with U and R already filled in, so students only read and record the current.
• Use only the 20 Ω series in step 2.
• Give sentence starters: "When the voltage doubles, the current…"
• Pair students so one operates the sliders and one records, then swap for step 4.

Stretch:

• Find R from the slope before reading it off the slider, then explain why converting mA to A matters.
• Predict the whole step 4 table from I = U/R before measuring.
• On the kit's Lab screen, tick Real bulbs (resistance rises as the bulb heats up), measure a bulb's current at two voltages, and explain why its I–V graph is not a straight line.
• Explore internal resistance with Ohm's law for a complete circuit.

English learners: the simulation is available in six languages. Create a second link in the student's language so the labels are familiar while the class discussion stays in English.

Standards alignment

This lesson fits typical middle and high school electricity units on current, voltage and resistance, such as the electricity topic of GCSE Physics or an introductory high school physics course. NGSS has no performance expectation dedicated to Ohm's law, so we don't claim one. The lesson does exercise three NGSS science and engineering practices: Planning and Carrying Out Investigations, Analyzing and Interpreting Data, and Using Mathematics and Computational Thinking.

To run it as a full lab write-up, see how to create a virtual lab activity. For more circuit ideas, see interactive physics lesson ideas.

FAQ

Why does the simulation use U instead of V for voltage?

U is the standard symbol for voltage in much of Europe. The law is the same: U = IR and V = IR describe the same relationship. Tell students before they start.

Why are the currents shown in milliamperes?

With resistances up to 1,000 Ω, most currents are well under one ampere. Milliamperes keep the numbers readable. Remind students that 1 A = 1,000 mA before they calculate a resistance.

Can students do this lesson on phones?

Yes. Students open the link without an account, and the sliders work on touch screens. A tablet or laptop makes it easier to hit exact values and read the table.

Does the simulation show non-ohmic components?

No. Its resistor always obeys Ohm's law. For a component whose resistance changes, use the real bulbs option on the circuit kit's Lab screen.