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Electrostatics & Electric Circuits: Evidence and Measurement

≈ 30 min
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Evidence and Measurement

Connect the claim to observable evidence and state what uncertainty or limitation remains.

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 — Evidence and Measurement: Two light spheres hang side by side. Both carry a negative charge. What will they do?

Physics: Motion, Waves & Electricity — Evidence and Measurement: 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 — Evidence and Measurement: 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 evidence and measurement lesson.

Which statement is the best evidence-led starting point for Electrostatics & Electric Circuits: Evidence and Measurement?