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🎯 You can now solve V, I and R problems in any order.
Next lesson: Charge, time and current — the Q = I × t formula.
08:00
Physics Lesson 3 — Continues from Lesson 2
Ohm's Law in Action
Solving real V, I and R problems
🔋
⚡
Ω
🧮
Learning Objectives (Spec 2.13 & 2.14):
Recall what voltage, current and resistance are (from Lesson 2).
Use V = I × R to find any of the three quantities.
Apply the 4-step method to solve circuit problems with units.
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Teacher Print Tools
⏱️ 40-Minute Pacing Guide (lighter than L2!)
Recap (4) → Arrival (4) → Starter (3) → I Do (5) → We Do (6) → Independent (8) → Exit (3) = 33 min of timed content + ~7 min for transitions.
⏱️ 4 min
Last Week's Recap
Recap Quiz – What Stuck from Lesson 2?
Instructions: Tap the answer you think is correct. Green = correct (locks the question). Red = try again. Goal: 5 out of 5 ✅
Q1. Current is the rate of flow of…?
Q2. The unit of resistance is…?
Q3. How is an ammeter connected in a circuit?
Q4. Which formula links voltage, current and resistance?
Q5. A current of 2 A flows through a 5 Ω resistor. What is the voltage?
🌟 Score check: 5/5 = ready to apply Ohm's Law today. 3–4 = quick re-cap as we go. 0–2 = grab the Knowledge Organiser sheet from the front.
⏱️ 4 min
Arrival Task
Arrival Task – Warm-Up Calculations
Instructions: Pick your tier. Show formula → substitute → answer + unit in your books. The VIR triangle is your friend!
1. Find V 🟢
I = 3 A, R = 2 Ω. Calculate the voltage.
V = I × R = 3 × 2 = 6 V
2. Find V 🟢
I = 4 A, R = 5 Ω. Calculate the voltage.
V = I × R = 4 × 5 = 20 V
3. Find V 🟢
A 10 Ω resistor has 2 A flowing through it. Calculate the voltage.
V = I × R = 2 × 10 = 20 V
1. Find V 🟠
I = 0.5 A, R = 8 Ω. Calculate V.
V = I × R = 0.5 × 8 = 4 V
2. Find I 🟠
V = 12 V, R = 4 Ω. Calculate I.
I = V ÷ R = 12 ÷ 4 = 3 A
3. Find R 🟠
V = 6 V, I = 2 A. Calculate R.
R = V ÷ I = 6 ÷ 2 = 3 Ω
1. Find R 🔵
A 230 V kettle draws 10 A. Calculate the resistance.
R = V ÷ I = 230 ÷ 10 = 23 Ω
2. Find I 🔵
V = 9 V, R = 18 Ω. Calculate I.
I = V ÷ R = 9 ÷ 18 = 0.5 A
3. Predict 🔵
If V stays the same and R doubles, what happens to I? Explain.
I halves. From I = V ÷ R, if R doubles and V stays the same, I must halve. (Inversely proportional.)
⏱️ 3 min
Starter
Starter: The VIR Triangle
Cover the letter you want to find — the rest is the formula.
The VIR Triangle
📝 Cover-Up Recall
Cover V → formula = ?
V = I × R
Cover I → formula = ?
I = V ÷ R
Cover R → formula = ?
R = V ÷ I
"To find R, I should do V × I."When you cover R on the triangle, V is on top and I is on the bottom — that means divide, not multiply. R = V ÷ I.
⏱️ 5 min
I Do
I Do: The 4-Step Method
Watch carefully. Every Ohm's Law calculation follows the same 4 steps. Examiners give marks for working — not just the final answer.
📋 The Question
A 9 V battery is connected to a torch. The torch bulb has a resistance of 3 Ω. Calculate the current flowing through the bulb.
Given: V = 9 V, R = 3 Ω. Find: I = ?
Step 1: Write the Formula
We want I. Cover I on the triangle: V is on top, R below.
I = V ÷ R
Step 2: Substitute
Plug the numbers in:
I = 9 ÷ 3
Step 3: Calculate
Do the maths:
I = 3
Step 4: Add the Unit
Current is measured in amps (A):
I = 3 A ✅
📝 Exam tip: Always show all 4 steps. A correct answer with no working can still lose marks. "3" is wrong — "3 A" is right.
"I just write the answer — that's all that matters."Examiners give 1 mark for the formula, 1 mark for substitution, and 1 mark for the answer with the correct unit. Skip any step and you skip a mark.
⏱️ 6 min
We Do
We Do: Calc Challenge 🧮
Together — class consensus first, then type the answer. Each pupil writes the full 4 steps in their books while we agree as a class.
Before each question: Turn to your partner and agree which formula to use. Cover the letter you need on the triangle.
Q1 – Find I
A 12 V battery is across a 4 Ω resistor.
A
Q2 – Find V
A current of 0.5 A flows through an 8 Ω resistor.
V
Q3 – Find R
A 6 V battery drives a current of 2 A.
Ω
📝 Reminder: In your books — write formula → substitute → answer + unit for each one. The class answer goes on the board.
⏱️ 8 min
Independent Work
Independent Work – Your Turn 💪
Pick your tier. Use the printed worksheet from your pack. Show all 4 steps for every question. Timer = 8 minutes.
📋 What's in Each Worksheet
🟢 Foundation (5 questions): All "find V" using V = I × R with whole numbers.
🟠 Middle (5 questions): Mix of find V, find I, find R. Decimals included.
🔵 Higher (5 questions): Real-world contexts (kettle, hairdryer, phone charger). Includes one "explain" question.
🪜 Stuck? The Scaffolding Sheet at the front of your pack has:
The VIR triangle
A worked example with all 4 steps
Sentence starters for "explain" questions
🏆 Success Criteria
Foundation: I can use V = I × R to find V when given I and R, with the correct unit.
Middle: I can rearrange V = I × R and use the correct form to find any of V, I, or R.
Higher: I can apply Ohm's Law to real-world contexts, show full working, and explain how V, I and R are related.
⚡ Speed tip: Don't redraw the triangle every time. Just write V = I × R at the top of your page and rearrange when you need to.
✅ Tick as you go
I wrote the formula every time
I substituted the numbers
I included the unit on every answer
⏱️ 3 min
Exit Ticket
Exit Ticket – Check Your Learning
Silent. No notes. Two questions to show you've got it.
Tip: Picture the VIR triangle. V on top, I × R on the bottom. Cover what you want to find.
🟢 I'm confident — I could teach this
🟡 Getting there — need more practice
🔴 I'm stuck — I need help
1) Write the formula that links V, I and R.
V = I × R
2) A current of 5 A flows through a 4 Ω resistor. Calculate the voltage. (Show formula → substitute → answer + unit.)
V = I × R = 5 × 4 = 20 V
1) A 12 V battery is connected to a 6 Ω resistor. Calculate the current.
I = V ÷ R = 12 ÷ 6 = 2 A
2) A bulb has 0.4 A flowing through it when 6 V is across it. Calculate the resistance.
R = V ÷ I = 6 ÷ 0.4 = 15 Ω
1) A UK kettle (230 V) draws a current of 10 A. Calculate the resistance of the heating element.
R = V ÷ I = 230 ÷ 10 = 23 Ω
2) A phone charger has resistance 25 Ω and supplies 5 V to the phone. Calculate the current and explain whether this is safe to touch (mains is dangerous above ~30 mA).
I = V ÷ R = 5 ÷ 25 = 0.2 A = 200 mA. This is well above 30 mA, BUT the charger steps voltage down from 230 V to 5 V — at 5 V the "push" is too weak to drive a dangerous current through your skin's high resistance. Safe to touch.
⚡ Next lesson: What if we wanted to know how much charge has flowed in a given time? You'll learn the equation Q = I × t.
Slide 1/8
PHYSICS · LESSON 3
Ohm's Law in Action
Spec 2.13 & 2.14 · IGCSE Single Science
FOUNDATION (U–1)
Name
Date
Tier Foundation 🟢
Learning Objectives
Recall what V, I and R mean and their units (from L2).
Use V = I × R to find the voltage when given I and R.
Show the formula, substitution, answer and unit for every calculation.
Success Criteria — tick as you go
I can write V = I × R from memory.
123
I can substitute numbers into V = I × R.
123
I always include the unit (V, A, or Ω) on my answer.
123
Key: 1 = need help · 2 = getting there · 3 = confident
Reflection
One thing I'm now confident with:
One thing I still need to practise:
PHYSICS · LESSON 3
Ohm's Law in Action
Spec 2.13 & 2.14 · IGCSE Single Science
MIDDLE (1–2)
Name
Date
Tier Middle 🟠
Learning Objectives
Recall the meaning and units of V, I and R.
Rearrange V = I × R to find any unknown (V, I or R).
Apply the 4-step method (formula → substitute → calculate → unit) to circuit problems.
Success Criteria — tick as you go
I can rearrange V = I × R using the VIR triangle.
123
I can find V, I or R given the other two.
123
I show all 4 steps and the unit every time.
123
Key: 1 = need help · 2 = getting there · 3 = confident
Reflection
The hardest type of question for me was:
My target for next lesson:
PHYSICS · LESSON 3
Ohm's Law in Action
Spec 2.13 & 2.14 · IGCSE Single Science
HIGHER (3–4)
Name
Date
Tier Higher 🔵
Learning Objectives
Recall and apply V = I × R fluently in all three forms.
Solve real-world Ohm's Law problems (kettles, hairdryers, phone chargers).
Explain qualitatively how V, I and R are related (e.g. doubling R halves I when V is fixed).
Success Criteria — tick as you go
I can solve V, I and R problems in any context.
123
I can convert mA → A and kΩ → Ω where needed.
123
I can explain how I changes when R or V changes.
123
Key: 1 = need help · 2 = getting there · 3 = confident
Reflection — challenge yourself
Where could V = I × R appear in everyday life?
Knowledge Organiser – Lesson 3: Ohm's Law in Action
Quantity
Symbol
Unit (Symbol)
What it means
Voltage
V
Volts (V)
The "push" from the battery — energy per coulomb of charge.
Current
I
Amps (A)
The rate of flow of charge through the circuit.
Resistance
R
Ohms (Ω)
How much a component opposes the flow of current.
The Three Forms of Ohm's Law
To find…
Cover on triangle
Formula
Voltage (V)
V (top)
V = I × R
Current (I)
I (bottom-left)
I = V ÷ R
Resistance (R)
R (bottom-right)
R = V ÷ I
The 4-Step Method
Step 1: Write the formula.
Step 2: Substitute the numbers.
Step 3: Calculate the answer.
Step 4: Add the unit (V, A, or Ω).
Examiners give marks for working — not just the final answer.
Recap Quiz – From Lesson 2
Name: _________________________ Score: ___ /5
1) Current is the rate of flow of: ☐ charge ☐ voltage ☐ resistance ☐ power
2) The unit of resistance is: ☐ Volts (V) ☐ Amps (A) ☐ Ohms (Ω) ☐ Coulombs (C)
3) An ammeter is connected: ☐ in series ☐ in parallel ☐ across the cell
4) The formula linking V, I and R is: ☐ V = I + R ☐ V = I − R ☐ V = I × R ☐ V = I ÷ R
5) A current of 2 A flows through a 5 Ω resistor. The voltage is: ☐ 2.5 V ☐ 7 V ☐ 10 V ☐ 0.4 V
Arrival Task – Warm-Up Calculations
Show formula → substitute → answer + unit for every question.
Foundation 🟢
1) I = 3 A, R = 2 Ω. Calculate V.
2) I = 4 A, R = 5 Ω. Calculate V.
3) A 10 Ω resistor has 2 A flowing through it. Calculate V.
Middle 🟠
1) I = 0.5 A, R = 8 Ω. Calculate V.
2) V = 12 V, R = 4 Ω. Calculate I.
3) V = 6 V, I = 2 A. Calculate R.
Higher 🔵
1) A 230 V kettle draws 10 A. Calculate R.
2) V = 9 V, R = 18 Ω. Calculate I.
3) Predict: if V stays the same and R doubles, what happens to I? Explain.
Starter – The VIR Triangle
Copy the triangle into your book. Then complete:
Cover V → formula = ____________________
Cover I → formula = ____________________
Cover R → formula = ____________________
Spot the mistake: "To find R, I should do V × I." What's wrong?
We Do – Calc Challenge (Class Work)
Show formula → substitute → answer + unit for each.
Q1. A 12 V battery is across a 4 Ω resistor. Calculate I.
Q2. A current of 0.5 A flows through an 8 Ω resistor. Calculate V.
Q3. A 6 V battery drives a current of 2 A. Calculate R.
Scaffolding Sheet – Keep this open as you work
1. The VIR Triangle
V ————— I × R
Cover the letter you want. The rest is the formula.
2. Worked Example (4 Steps)
Q: A 9 V battery is connected to a 3 Ω torch bulb. Calculate I.
Step 1: Formula → I = V ÷ R
Step 2: Substitute → I = 9 ÷ 3
Step 3: Calculate → I = 3
Step 4: Unit → I = 3 A ✅
3. Sentence Starters for "Explain"
"Using V = I × R…"
"When R doubles and V stays the same, I…"
"This is because current is the rate of flow of charge, so…"
4. Common Units
Voltage = volts (V) · Current = amps (A) · Resistance = ohms (Ω)
Need to convert? 1 mA = 0.001 A; 1 kΩ = 1000 Ω.
Independent Work – Foundation 🟢
Use V = I × R. Show formula → substitute → answer + unit.
1. I = 2 A, R = 3 Ω. Calculate V.
2. I = 5 A, R = 4 Ω. Calculate V.
3. I = 1 A, R = 12 Ω. Calculate V.
4. A bulb has 3 A flowing through it and a resistance of 6 Ω. Calculate the voltage across it.
5. A heater has 4 A flowing through it and a resistance of 25 Ω. Calculate the voltage across it.
Independent Work – Middle 🟠
Choose the correct form of V = I × R. Show all 4 steps.
1. V = 18 V, I = 3 A. Calculate R.
2. V = 9 V, R = 6 Ω. Calculate I.
3. I = 0.4 A, R = 20 Ω. Calculate V.
4. A lamp has 0.6 A through it when 12 V is across it. Calculate R.
5. A 24 V supply is connected to a 100 Ω resistor. Calculate I.
Independent Work – Higher 🔵
Real-world Ohm's Law. Show all 4 steps. Watch units (mA → A, kΩ → Ω).
1. A UK kettle (230 V) has a heating element of resistance 46 Ω. Calculate the current.
2. A hairdryer draws 5 A from the 230 V mains. Calculate its resistance.
3. A phone charger supplies 5 V and the phone draws 500 mA. Calculate the resistance of the phone (convert mA to A first!).
4. A torch uses two 1.5 V cells in series (so 3 V total) and the bulb has resistance 6 Ω. Calculate the current.
5. (Explain) Two students use the same 12 V battery. Student A uses a 3 Ω resistor. Student B uses a 6 Ω resistor. Without calculating, explain whose circuit will have the larger current. Then calculate both to check.
1) A UK kettle (230 V) draws a current of 10 A. Calculate the resistance of the heating element.
2) A phone charger has resistance 25 Ω and supplies 5 V. Calculate the current and explain whether the charger is safe to touch (mains is dangerous above ~30 mA).
