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Electrostatics & Electric Circuits: Worked Reasoning

≈ 30 min
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Worked Reasoning

Make each reasoning step visible: identify the knowns, choose the governing idea, apply it and check the result.

This extension applies that lens specifically to Electrostatics & Electric Circuits.

Two kinds of charge

Matter contains two kinds of electric charge: positive (carried by protons) and negative (carried by electrons). The rule for how they interact is short:

  • Like charges repel (push apart).
  • Unlike charges attract (pull together).

When you rub a plastic ruler on your sleeve it can pick up tiny bits of paper. Rubbing transfers electrons from one surface to the other. No charge is created or destroyed - it is only moved. This is conservation of charge: the total charge before and after stays the same.

Making charge flow: current, emf and potential difference

In a circuit a cell (battery) pushes charge around a conducting loop.

  • Current (II) is the rate of flow of charge, measured in amperes (A\text{A}):
I=QΔtI = \frac{Q}{\Delta t}

where QQ is charge in coulombs (C\text{C}).

  • Emf (electromotive force) is the total energy the cell gives each coulomb of charge to move it around the whole circuit, measured in volts (V\text{V}).
  • Potential difference (VV) across a component is the energy transferred per coulomb as charge passes through that component:
V=WQV = \frac{W}{Q}
  • Resistance is the opposition a component offers to the flow of charge. A larger resistance means it is harder for charge to flow for a given push.

Physics: Motion, Waves & Electricity — Worked Reasoning: Two light spheres hang side by side. Both carry a negative charge. What will they do?

Physics: Motion, Waves & Electricity — Worked Reasoning: A charge of 6 C6\,\text{C} flows through a torch bulb in 3 s3\,\text{s}. Calculate the current in the bulb, in amperes.

Physics: Motion, Waves & Electricity — Worked Reasoning: As charge flows through a resistor, 24 J24\,\text{J} of energy is transferred for every 4 C4\,\text{C} that passes through it. Calculate the potential difference across the resistor, in volts.

Name the original topic being extended by this worked reasoning lesson.

Which statement is the best evidence-led starting point for Electrostatics & Electric Circuits: Worked Reasoning?