Physics Lesson 2c — Take 2

Ohm's Law Practical — Done Properly

Rearrange. Read. Calculate. 🔬

🔁 ⚡ 🎯

Today's Focus (Spec 2.13 & 2.14):

✓

Rearrange V = I × R to find R or I (covering the triangle).

✓

Calculate resistance from your own measured V and I.

✓

Show working: Formula → Substitute → Answer + Unit.

📌 Why we're doing this again: Last week the sim glitched and time ran out. Today: same kit, sharper plan. You already know how to build a circuit — today we focus on the maths and the readings. You've got this.

🖨️ Teacher Print Tools — Pupil Packs

⏱️ 3 min

Arrival Task

Recall (×3) + Today's Bridge

Instructions: Three quick recall questions from last week, then one question that bridges into today's focus. Short answers — one word or one number is fine.

1. Recall 🟢

Fill the gap: V = I × ___

R (resistance, in ohms Ω).

2. Recall 🟢

The ammeter goes in series or parallel?

Series — break the wire, drop it in the loop.

3. Recall 🟢

What unit is current measured in?

Amps (A).

1. Recall 🟠

I = 2 A, R = 5 Ω. Find V.

V = I × R = 2 × 5 = 10 V

2. Recall 🟠

Where does the voltmeter go, and what does it measure?

In parallel across the component. It measures voltage (V).

3. Recall 🟠

Name two components you drag onto the PhET workspace to start a circuit.

Battery and bulb (plus wires to connect them).

1. Recall 🔵

Why must the ammeter be in series, not parallel?

Current must flow through the ammeter to be counted — only series puts it inside the loop.

2. Recall 🔵

V doubles from 6 V to 12 V (same R). What happens to I?

I doubles. (I = V ÷ R — V doubles, R unchanged → I doubles.)

3. Recall 🔵

V = 8 V, I = 4 A. Find R.

R = V ÷ I = 8 ÷ 4 = 2 Ω

🌉 4. Today's Bridge — Lead-in Question

Last week, some of you got stuck when you'd measured V and I on your circuit, but didn't know how to work out R.

Have a go: If V = 12 V and I = 4 A, which formula would you use to find R — and what answer do you get?

R = V ÷ I = 12 ÷ 4 = 3 Ω. That's exactly the skill we're sharpening today.

⏱️ 4 min

Starter

Starter: The Mystery Box 🎁

Instructions: Two values are shown. One is missing (highlighted gold). Use the triangle to find it. Type your answer, click Check, then hit 🔄 New Mystery for the next one. Aim for 3 in a row 🔥 for a streak bonus.

The VIR Triangle

Cover the ? letter on the triangle. What's left is your formula.

Rule of thumb

Finding V → multiply (I × R).
Finding I or R → divide (V on top).

⏱️ 4 min

I Do

I Do: Three Ways to Use the Triangle

Just watching: Pens down. I'll work through all three rearrangements. Notice — they all follow the same 3 steps.

① Find R (today's main skill)

Given: V = 10 V I = 2 A

Step 1 — Formula: Cover R → R = V ÷ I

Step 2 — Substitute: R = 10 ÷ 2

Step 3 — Answer + Unit: R = 5 Ω ✅

② Find I

Given: V = 12 V R = 4 Ω

Step 1: Cover I → I = V ÷ R

Step 2: I = 12 ÷ 4

Step 3: I = 3 A ✅

③ Find V

Given: I = 0.5 A R = 12 Ω

Step 1: Cover V → V = I × R

Step 2: V = 0.5 × 12

Step 3: V = 6 V ✅

🧠 The Memory Rule

Finding V? → MULTIPLY (V = I × R)

Finding I? → DIVIDE (V ÷ R)

Finding R? → DIVIDE (V ÷ I)

V sits on top of the triangle, so whenever you divide, V goes on top of the fraction.

📋 Always Show:

Formula → Substitute → Answer + Unit. Even a wrong final calculation earns marks if the formula and substitution are right.

⚠️ Three traps to avoid:

• Multiplying V and I to find R (R = V × I is wrong)

• Adding or subtracting — Ohm's law only uses × and ÷

• Forgetting the unit (an answer of "5" without "Ω" loses marks)

🌟 Today's mission: Measure V and I on your PhET circuit, then use ① above to calculate R.

⏱️ 5 min

We Do

We Do: Three Calcs — Same 3 Steps

Together: Same 3 steps from the I Do. Formula → Substitute → Answer + Unit. Write each one in your book — I'll check as I walk round.

Q1 — Find R 🟢

A bulb in PhET. You measure V = 8 V and I = 2 A. Find R.

Type R = Ω

Cover R on the triangle. What's left? V ÷ I. So R = 8 ÷ 2.

Q2 — Find I 🟠

A 10 Ω resistor connected to a 20 V battery. Find I.

Type I = A

Cover I on the triangle. What's left? V ÷ R. So I = 20 ÷ 10.

Q3 — Find R 🟠

A motor in PhET. You measure V = 18 V and I = 3 A. Find R.

Type R = Ω

Same routine as Q1. Cover R on the triangle → R = V ÷ I = 18 ÷ 3.

🌟 Stretch (if you nailed Q3): Same routine, but with a decimal. A torch bulb has V = 3 V and I = 0.5 A. Find R. (Tip: dividing by 0.5 is the same as multiplying by 2.)

🎯 Spot the Error

A pupil writes: "V = 6 V, I = 2 A, so R = 6 × 2 = 12 Ω." Which mistake did they make?

🧠 Reminder

Finding V → multiply.
Finding I or R → divide (V always on top).

🏠 Real-world link

A UK kettle on 230 V mains draws about 10 A. What's its resistance? (Same skill — divide V ÷ I = 23 Ω.)

⏱️ 12 min — PHASE 1: BUILD & RECORD

Independent · Phase 1 of 2

Phase 1: Build the Circuit, Record the Readings

Phase 1 of 2: Pick your level. Build the circuit in PhET. Type the meter readings into the table. When every row is filled, press → Next to move to Phase 2: Calculations.

📝 Your name:

🚀 Launch Sim

Sim by PhET Interactive Simulations, University of Colorado Boulder. Free to use under CC-BY licence.

🟢 Foundation — Build & Read

Build: 1 battery + 1 bulb + ammeter (in series) + voltmeter (across the bulb).

Step 1: Set battery to 9 V. Read meters and type the numbers in.

Step 2: Set battery to 4.5 V. Read meters again.

Step 3: Use R = V ÷ I to fill in the resistance column.

Battery	V (volts)	I (amps)	R = V÷I (Ω)
9 V
4.5 V

🌟 Quick Q: Did the resistance stay roughly the same? (It should — the bulb's R doesn't change much.)

✅ Readings in? Press → Next for Phase 2: Calculations.

⏱️ 8 min — PHASE 2: CALCULATIONS

Independent · Phase 2 of 2

Phase 2: Use Your Readings to Calculate

Phase 2 of 2: Your readings from Phase 1 are shown below — use them with V = I × R (and the triangle) to answer each question. When you've finished, hit Submit for marking + a personalised report.

⚡ Calculations (use the readings above + the triangle)

Q1. If V = 6 V and I = 2 A, what is R? Ω

Q2. If I = 3 A and R = 4 Ω, what is V? V

Q3. If V = 10 V and R = 5 Ω, what is I? A

✅ When you finish: Put your hand up. Mr Roper will check your work and you'll do the exit ticket.

⏱️ 5 min

Exit Ticket

Exit Ticket — Climb the Confidence Ladder 🪜

Instructions: No notes. No sim. Answer in your books. Start at the bottom rung — get as high as you can. Each rung you complete = one grade tier proven.

Tap how confident you feel — this prints onto your evidence report.

Grade 5

6. A bulb's voltage doubles from 6 V to 12 V (same bulb). The original current was 2 A. What's the new current? Explain in one sentence.

R = V ÷ I = 6 ÷ 2 = 3 Ω (R doesn't change). New I = V ÷ R = 12 ÷ 3 = 4 A. When V doubles and R stays the same, I doubles too.

Grade 3–4

5. V = 9 V, I = 0.3 A. Find R.

R = V ÷ I = 9 ÷ 0.3 = 30 Ω

Grade 2

4. V = 12 V, R = 6 Ω. Find I.

I = V ÷ R = 12 ÷ 6 = 2 A

Grade 1

3. I = 3 A, R = 4 Ω. Find V.

V = I × R = 3 × 4 = 12 V

Grade U–1

2. Match the letter to the unit: V → ___ I → ___ R → ___ (volts / amps / ohms)

V → volts, I → amps, R → ohms (Ω).

Start

1. What is the unit of resistance?

Ohms (Ω).

⚡ Next lesson: Voltage across components in parallel circuits — and why your house wiring is never in series.

Knowledge Organiser: Ohm's Law (Recap)

Use this: Read it before starting. Refer back during the practical. Cover it for the exit ticket.

Concept	Details
Voltage (V)	The "push" — energy per coulomb. Volts (V). Voltmeter — in parallel.
Current (I)	Rate of flow of charge. Amps (A). Ammeter — in series.
Resistance (R)	Slows the flow. Ohms (Ω).
Ohm's Law	V = I × R
Rearranged	I = V ÷ R R = V ÷ I
VIR Triangle	V on top, I × R on bottom. Cover what you need.
1 Amp	1 coulomb of charge per second.
UK Mains	230 V.

🧠 Memory Tricks

Finding I or R? You DIVIDE.

Finding V? You MULTIPLY.

Always: Formula → Substitute → Answer + UNIT.

Arrival – Foundation 🟢

Three recall questions from last week, then one bridge into today.

1. Fill the gap: V = I × ___

2. Does the ammeter go in series or parallel?

3. What unit is current measured in?

🌉 4. Today's Bridge: If V = 12 V and I = 4 A, which formula would you use to find R, and what answer do you get?

Arrival – Middle 🟠

Three recall questions from last week, then one bridge into today.

1. I = 2 A, R = 5 Ω. Find V.

2. Where does the voltmeter go, and what does it measure?

3. Name two components you drag onto the PhET workspace.

🌉 4. Today's Bridge: If V = 12 V and I = 4 A, which formula would you use to find R, and what answer do you get?

Arrival – Higher 🔵

Three recall questions from last week, then one bridge into today.

1. Why must the ammeter be in series, not parallel?

2. V doubles from 6 V to 12 V (same R). What happens to I?

3. V = 8 V, I = 4 A. Find R.

🌉 4. Today's Bridge: If V = 12 V and I = 4 A, which formula would you use to find R, and what answer do you get?

Starter – The Mystery Box 🎁

Two values are given. The third is missing. Use the VIR triangle to find it. Show Formula → Substitute → Answer + Unit for each.

Mystery 1 — Find R
V = 10 V, I = 2 A, R = ?

Formula: ____________
Sub: ____________
Answer: __________ Ω

Mystery 2 — Find I
V = 12 V, R = 4 Ω, I = ?

Formula: ____________
Sub: ____________
Answer: __________ A

Mystery 3 — Find V
I = 0.5 A, R = 8 Ω, V = ?

Formula: ____________
Sub: ____________
Answer: __________ V

Rule of thumb: Finding V → multiply (I × R). Finding I or R → divide (V on top).

Independent Practical – Foundation 🟢

Aim: Build a circuit. Read the meters. Calculate the resistance.

Setup

Build: 1 battery + 1 light bulb + 1 ammeter (in series) + 1 voltmeter (across the bulb).

Section A: Take Readings

Battery setting	V (volts)	I (amps)	R = V ÷ I (Ω)
9 V
4.5 V

Did the resistance stay roughly the same?

Section B: Calculations (show your working)

1. If V = 6 V and I = 2 A, what is R?

2. If I = 3 A and R = 4 Ω, what is V?

3. If V = 10 V and R = 5 Ω, what is I?

4. (Stretch) A bulb with R = 6 Ω is in a 12 V circuit. What is the current?

Section C: Quick Check

5. What does an ammeter measure, and where do you put it in a circuit?

Independent Practical – Middle 🟠

Aim: Investigate how current changes when you change the voltage.

Setup

Build: 1 battery (variable) + 1 resistor (set to ~10 Ω) + ammeter (in series) + voltmeter (across the resistor).

Section A: Investigation

V (set on battery)	I (read meter, A)	R = V ÷ I (Ω)
3 V
6 V
9 V
12 V

1. What happens to I when you double V?

2. Did your calculated R stay roughly the same? Why does that make sense?

Section B: Calculations

3. A 9 V battery is connected to a 3 Ω resistor. Calculate I.

4. V = 12 V, I = 0.5 A. Find R.

5. A lamp has R = 15 Ω and I = 0.4 A. Find V.

6. (Grade 3 stretch) Same lamp, V doubles to 12 V. New current?

Independent Practical – Higher 🔵

Aim: Investigate what happens to current and voltage when you add resistors in series.

Setup

Build: battery (12 V) + 2 resistors in series (R₁ ≈ 10 Ω, R₂ ≈ 20 Ω) + ammeter + voltmeter (move it to read across each resistor in turn).

Section A: Investigation

Setup	V total	V across R₁	V across R₂	I (anywhere)
R₁ alone (12 V battery)			—
R₁ + R₂ in series (12 V)

1. What happened to the current when you added R₂?

2. Do V₁ + V₂ add up to V total? (They should.)

3. Explain in terms of charge flow why current is the same everywhere in a series circuit. (Grade 5)

Section B: Exam-Style Calculations

4. (3 marks) A hairdryer runs on 230 V mains and draws 10 A. Calculate its resistance.

5. (3 marks) Two resistors (10 Ω + 20 Ω) in series with a 6 V battery. Calculate the current.

6. (Grade 5 — 4 marks) A resistor: V = 8 V, I = 0.4 A. The voltage is increased to 12 V (resistor unchanged). Calculate the new current. Show your reasoning.

Exit Ticket — Climb the Confidence Ladder 🪜

Name: _________________________ Date: _____________

Start at Rung 1. Get as high as you can. Each rung = one grade tier proven.

Rung 1 (Start): What is the unit of resistance?

Rung 2 (Grade U–1): Match — V → ____, I → ____, R → ____ (volts / amps / ohms)

Rung 3 (Grade 1): I = 3 A, R = 4 Ω. Find V.

Rung 4 (Grade 2): V = 12 V, R = 6 Ω. Find I.

Rung 5 (Grade 3–4): V = 9 V, I = 0.3 A. Find R.

Rung 6 (Grade 5): A bulb's voltage doubles from 6 V to 12 V (same bulb). Original I = 2 A. Find the new I. Explain in one sentence.

Highest rung I climbed today: ______ Confidence: 🟢 / 🟡 / 🔴 (circle one)

⚡ Evidence Report — Ohm's Law Practical

Progress Schools • Lesson 2b • IGCSE Physics Spec 2.13 & 2.14 (V = I × R)

Pupil: —

Tier: —

Date: —

Teacher: Mr Roper

Final score: —

Question-by-question breakdown

Question	Pupil's answer	Correct ans.	Mark	Diagnosis

👁️ TA Brief — This Slide

🎯 Random Pupil Picker

💡 Use the Triangle

📊 Marking Complete!

✅ Question Breakdown

🎯 Things to Watch For

🚀 Your Next Step

Lesson Complete!

Ohm's Law Practical — Done Properly

🖨️ Teacher Print Tools — Pupil Packs

Recall (×3) + Today's Bridge

1. Recall 🟢

2. Recall 🟢

3. Recall 🟢

1. Recall 🟠

2. Recall 🟠

3. Recall 🟠

1. Recall 🔵

2. Recall 🔵

3. Recall 🔵

🌉 4. Today's Bridge — Lead-in Question

Starter: The Mystery Box 🎁

The VIR Triangle

Rule of thumb

🎁 THE MYSTERY BOX

I Do: Three Ways to Use the Triangle

① Find R (today's main skill)

② Find I

③ Find V

🧠 The Memory Rule

📋 Always Show:

We Do: Three Calcs — Same 3 Steps

Q1 — Find R 🟢

Q2 — Find I 🟠

Q3 — Find R 🟠

🎯 Spot the Error

🧠 Reminder

🏠 Real-world link

Phase 1: Build the Circuit, Record the Readings

🟢 Foundation — Build & Read

🟠 Middle — Investigate V vs I

Pattern Check

🔵 Higher — Series Resistors

Reasoning

Phase 2: Use Your Readings to Calculate

⚡ Calculations (use the readings above + the triangle)

⚡ Calculations

⚡ Exam-Style Calculations

Exit Ticket — Climb the Confidence Ladder 🪜

Knowledge Organiser: Ohm's Law (Recap)

🧠 Memory Tricks

Arrival – Foundation 🟢

Arrival – Middle 🟠

Arrival – Higher 🔵

Starter – The Mystery Box 🎁

Independent Practical – Foundation 🟢

Setup

Section A: Take Readings

Section B: Calculations (show your working)

Section C: Quick Check

Independent Practical – Middle 🟠

Setup

Section A: Investigation

Section B: Calculations

Independent Practical – Higher 🔵

Setup

Section A: Investigation

Section B: Exam-Style Calculations

Exit Ticket — Climb the Confidence Ladder 🪜

⚡ Evidence Report — Ohm's Law Practical

Question-by-question breakdown

🎯 Misconceptions identified

🚀 Your most important next step

👨‍🏫 Teacher comment