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Grade 11 Science · Problem type
Motor or generator?
Use this for “A generator turns. What energy change happens, and why does it make a current?”
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Which way does the energy go?
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Assumptions
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A motor: the current’s magnetic field and the magnet’s field push on each other, so electrical energy becomes motion.
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A generator: a coil turning in a magnetic field has a changing flux, so motion becomes electrical energy.
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They are the same device run in opposite directions.
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Related lessons
Magnetic fields, magnetic forces and electromagnetic induction
Main lesson
Flux from a changing field
Use this for “A 200-turn coil of area 0.02 m² sits in a field that grows from 0.1 T to 0.5 T in 0.1 s. What emf is induced?”
The force on a current in a magnetic field
Use this for “A 0.25 m wire carrying 5 A crosses a 0.40 T field at 90°. What force acts on it? What if the angle is 30°?”
The force on a moving charge
Use this for “A 5 μC charge moves at 400 m/s across a 0.3 T field. What force acts on it? What if it moves at 30° to the field?”
A charge circling in a magnetic field
Use this for “A proton moves at 3 × 10⁶ m/s square to a 0.2 T field. What force acts on it, what is the radius of its circle, and how long is one lap?”
A transformer
Use this for “A transformer steps 120 V down with 400 primary turns and 20 secondary turns. What voltage comes out, and what current if 0.1 A goes in?”
Magnetic poles and field lines
Use this for “One magnet is turned round. How do the size and direction of the force change?”