How can a magnet and current turn a motor?

Situation and prediction

In a toy car the battery stays still while the wheel turns. A motor sits between them. What inside converts electrical energy into motion? Before reading, sketch ‘battery → current → magnetic effect → rotation’ and mark where some energy may become heat.

New words, step by step

A wire carrying current in a magnetic field can experience a force. Forces on opposite sides of a rotating coil produce torque, an effect that turns an axle. The rotor turns and the stator stays still. In a simple brushed motor a commutator changes the coil connection every half-turn so turning continues in the same direction. This is a qualitative model; real motors have losses.

Working through supplied data

Supplied energy budget: a battery transfers 10 J, 6 J becomes useful mechanical work, and 4 J becomes heating and other losses. Useful fraction 6/10 = 0.6, or 60%. This is not the rated efficiency of all motors. A stalled motor can still draw current and heat its windings.

A safe check

Study a transparent teaching model or a diagram instead of constructing a motor. Identify the coil, magnet, axle and power source, then trace one half-turn. Use a ready-made low-voltage kit only as instructed and supervised; do not open mains appliances or stop a spinning motor with your hand.

Where the reasoning breaks

A permanent magnet does not ‘fuel’ the motor. It supplies a field; the battery supplies electrical energy, some of which becomes motion. A fixed pair of forces alone does not guarantee endless rotation without commutation or another design.

Support diagram

Transfer to a new case

Two identical motors lift a load to the same height, but one gets warmer. Which measurements would let you compare efficiency? Why is case temperature alone insufficient for a numerical answer?

Check your understanding

Close the explanation and say in your own words what was really observed, which figures were supplied for teaching, and which conclusion remains a prediction. Change one condition and predict the result before rereading. If it disagrees, find the first step where your reasoning parted from the diagram. A strong answer names the model’s limits rather than just a correct word or number. You can do this check on paper, without equipment or registration.

Lab notebook entry

Add a page to My World Lab Notebook. Record the question, a prediction made before testing, a sketch and a table of conditions. Keep actual observations separate from supplied teaching numbers. In the final line say what changed, what stayed constant, what the evidence supports and what it does not yet prove. If you did no experiment, label the work ‘calculation from supplied data’ or ‘prediction’, never ‘measured’.

Next lesson: Why does moving a magnet deflect a meter?