Year 7 Science · Unit 3 · Lesson 15
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Learning Goals
Real-world context
At a scrapyard near Newcastle, a crane uses a large flat electromagnet to lift old cars and steel beams. The operator drives the crane over a car, switches the magnet on to grab it, swings it to the crusher, then switches the magnet off to drop it. The same magnet handles dozens of cars every hour, picking each one up and dropping it on command.
(a) Explain what the operator changes in the circuit to make the magnet "let go" of the car. Why does a permanent magnet not work for this job?
(b) The yard wants the crane to lift heavier loads. Suggest two changes engineers could make to the electromagnet to increase its strength.
Fair test plan
A student wants to test whether more turns of wire make an electromagnet stronger. Complete the fair test plan below by filling in the empty boxes.
Why is it important to change only ONE variable at a time?
1. Describe two different ways you could map the invisible magnetic field around a bar magnet. For each method, explain what you would actually see or do.
2. A student tests their electromagnet but changes the number of turns AND the number of cells at the same time. The magnet gets stronger. Explain why the student cannot be sure which change caused the result.
Wrap Up
In one sentence, what was the main idea of this lesson?