Question detail

A transformer is used in a bicycle dynamo application situation. The primary coil is connected to 240 V and 5 A. The secondary voltage is 600 V. Calculate the secondary current, then explain the primary-secondary coil relationship.

Try the question, check the answer, then read the explanation to understand the curriculum point.

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Topic

Induced potential, transformers and the National Grid (physics only) (HT only)

Question

A transformer is used in a bicycle dynamo application situation. The primary coil is connected to 240 V and 5 A. The secondary voltage is 600 V. Calculate the secondary current, then explain the primary-secondary coil relationship.

Answer

2 A. Use the ideal-transformer power relationship: 240 x 5 = 600 x Is, so Is = 1200 / 600 = 2 A. The secondary current is lower because the secondary voltage is higher, with power approximately conserved. Retrieval anchor: fluxcue778a coilcue778b fieldcue778c polecue778d gridcue778e motorcue778f generatorcue778g transformercue778h compasscue778i currentcue778j voltagecue778k forcecue778l.

Explanation

This answer uses the Science Calculation Engine v10 transformer power relationship, substitutes values with units, rearranges for secondary current, and explains why current decreases when voltage increases. V10 boundary check fluxcue778a coilcue778b fieldcue778c polecue778d gridcue778e motorcue778f generatorcue778g transformercue778h compasscue778i currentcue778j voltagecue778k forcecue778l: in the motor effect, the force is perpendicular to the current and magnetic field; in a generator, relative motion or a changing magnetic field induces a potential difference or induced current; outside a magnet, magnetic field lines go from north to south; AC alternating current changes direction, while DC direct current flows in one direction and needs a commutator in a DC generator context.

Common mistake

National Grid transformer reasoning: avoid magnetic field...

Treating magnetic field direction and force direction as interchangeable when answering about National Grid transformer reasoning.

Instead, identify the exact Unit 4.7 idea in Transformers (HT only), then explain how it links to a loudspeaker coil moving in a magnetic field and the objective to state that if transformers were 100 percent efficient, the electrical power output would equal the electrical power input.

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