Science lesson plan · 12th grade (Year 13 in England) · 60 minutes
Transformers and the National Grid
Electricity and magnetism
CCSS NGSS.HS-PS2-5CCSS NGSS.HS-PS3-3England: GCSE Physics: Magnetism and electromagnetism (transformers)England: GCSE Combined Science: Energy (the National Grid)
Objective and success criteria
Students will: Transformers and the National Grid.
- I can answer questions on today's skill on my own, without help.
- I can explain each step and say why it works.
- I can check my answer and spot a mistake.
Before and after
Needs first: The motor effect (F = B I l) and Fleming's left-hand rule; Power and energy in circuits (P = I²R, E = QV)
Leads to: the next skill in this area.
Materials: Circuit kits (cells, wires, bulbs), Circuit symbol cards, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).
Warm-up · 6 min
- Quick retrieval from earlier learning (The motor effect (F = B I l) and Fleming's left-hand rule; Power and energy in circuits (P = I²R, E = QV)). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- A wire 0.1 m long carrying 3 A sits at right angles to a magnetic field of 0.2 T. What is the force on the wire, in N? → 0.06 NPrompt: F = B × I × l
- A current of 1 A flows through a 5 Ω resistor. What power is transferred, in W? → 5 WPrompt: P = I² × R
- A 0.1 m wire carrying 2 A at right angles to a magnetic field feels a force of 0.1 N. What is the magnetic flux density, in T? (Give 2 decimal places.) → 0.5 TPrompt: Rearrange F = B I l to find B.
Hook · 6 min
- Show a circuit with a gap and ask why the bulb doesn't light.
- Share the objective: Transformers and the National Grid. Read the success criteria together.
I do: model it · 12 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: A transformer has 500 turns on the primary coil and 2500 turns on the secondary. The input voltage is 24 V. What is the output voltage, in V? (Vp ÷ Vs = Np ÷ Ns)
- Step 1: 24 × 2500 ÷ 500 = 120
- Step 2: So the answer is: 120 V
- Answer: 120 V
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 12 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- A transformer has 200 turns on the primary coil and 800 turns on the secondary. The input voltage is 24 V. What is the output voltage, in V? (Vp ÷ Vs = Np ÷ Ns) → 96 VPrompt: More turns on the secondary means a higher output voltage.
- A 100 % efficient transformer has an input of 230 V and 5 A. The output voltage is 46 V. What is the output current, in A? (Vp × Ip = Vs × Is; give 2 decimal places) → 25 APrompt: Power in = power out.
You do: independent practice · 17 min
- Students work on the student sheet. Circulate and check the first two answers of every student early.
- Students who finish: write a question of their own for a partner, with the answer.
The 8 questions are on the student sheet below, with answers in the key.
Exit ticket · 7 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- Why does the National Grid transmit electricity at very high voltages? (High voltage makes electricity travel faster / Homes need very high voltages / A high voltage means a low current, so less energy is lost heating the cables / It makes the cables lighter) → A high voltage means a low current, so less energy is lost heating the cablesPrompt: Power lost in cables = I² R.
- A 100 % efficient transformer has an input of 25000 V and 5 A. The output voltage is 275000 V. What is the output current, in A? (Vp × Ip = Vs × Is; give 2 decimal places) → 0.45 APrompt: Power in = power out.
Watch out for
- Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
- Remembering facts without the reason: ask "why?" and "what is the evidence?"
Support and stretch
Support
- Review first: The motor effect (F = B I l) and Fleming's left-hand rule.
- Use concrete materials: circuit kits (cells, wires, bulbs).
- Give the first step of each question, or a partly worked example to finish.
- Pair with a confident partner for the guided practice.
Stretch
- Explain a common mistake in writing and how to fix it.
- Write a word problem that uses today's skill, then solve a partner's.
Homework and more practice
Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-12.
Free lesson plan from eurekami.com/lesson-plan-builder