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3
I = V/R.
Class 9 · English Medium · Cambridge · Physics
Electricity, magnetism and circuits
Analyse current, potential difference, resistance and induction safely on paper.
Shared cross-level core and stretch unit. Start with the core questions, then use the stretch example for deeper work. The same unit is available in related class and board pathways; it is not a full grade-specific or examination-specification course. A teacher should select the appropriate depth and further topics.
Learn the idea
Current is charge per time; potential difference is energy transferred per charge. For an ohmic resistor at constant temperature, V = IR. Series currents are equal; parallel branches share potential difference. Electromagnetic induction requires changing magnetic flux linkage, not merely a stationary field.
Worked example
A 12 V supply across 6 Ω gives 2 A and 24 W. Two series resistors 2 Ω and 4 Ω have total 6 Ω. Two equal 6 Ω resistors in parallel have total 3 Ω.
- Draw the circuit and identify connections.
- Apply charge and energy conservation.
- Check that power and units are sensible.
Stretch example
An ideal transformer has Vs/Vp = Ns/Np. For Vp = 240 V, Np = 1200 turns and Ns = 60 turns, Vs = 12 V. This is a paper model, not instructions to connect mains electricity.
Your written practice
Show your working on paper and enter your answer here. If it does not match, compare the model and try again.
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11
Series resistances add.
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10
P = VI.
Write in your own words. A guardian or teacher should review this response.
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It provides another conducting path, increasing total current at the same voltage.
Compare at fixed supply voltage.
Write in your own words. A guardian or teacher should review this response.
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No; its magnetic flux linkage is not changing.
State the changing-flux condition.
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4
20 × 100/500.
Write in your own words. A guardian or teacher should review this response.
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A changing magnetic field links the secondary and induces an emf; steady DC does not provide that continuing change.
Explain induction, not just a turns ratio.
Circuit on paper
Compare one series and one parallel resistor circuit with a fictional 6 V supply.
Review with a guardian or teacher
- Show every resistance.
- Calculate currents consistently.
- Use diagrams or simulation only.
Keep your work on paper or in a local file. This page does not upload it or automatically grade the project.
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