Question detail

A transformer is used in a National Grid substation exam-command 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 National Grid substation exam-command 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: fluxcue660a coilcue660b fieldcue660c polecue660d gridcue660e motorcue660f generatorcue660g transformercue660h compasscue660i currentcue660j voltagecue660k forcecue660l.

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 fluxcue660a coilcue660b fieldcue660c polecue660d gridcue660e motorcue660f generatorcue660g transformercue660h compasscue660i currentcue660j voltagecue660k forcecue660l: 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 motors and generators

Treating motors and generators as interchangeable when answering about National Grid transformer reasoning.

Instead, identify the exact Unit 4.7 idea in Microphones (HT only), then explain how it links to a step-down transformer for a low-voltage device and the objective to describe how pressure variations in sound waves are converted into variations in current in electrical circuits.

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