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Current and Charge

Linking current to the flow of charge with Q = I × t.

  • Define and explain Current and Charge in your own words
  • Use key terms such as current accurately
  • Apply what you have learned to new examples and questions
  • Avoid the common mistakes learners make with this topic

Electricity powers the modern world, and it obeys beautifully simple rules. Master current, voltage and resistance, and you can predict what any circuit will do before you even build it.

This lesson focuses on Current and Charge: linking current to the flow of charge with Q = I × t.

Definition: Current and Charge

Linking current to the flow of charge with Q = I × t.

Key ideas

Current is moving charge

In metals, current is a flow of electrons. Charge Q = current × time, so 2 A for 3 s moves 6 C of charge. An ammeter measures current and is connected in series; conventional current is drawn as flowing from positive to negative, opposite to the electron flow.

Voltage, current and resistance are linked by V = IR

Voltage drives current through resistance like pressure drives water through a pipe. Doubling the voltage doubles the current through a fixed resistor. Ohmic conductors give a straight-line current–voltage graph through the origin — this is Ohm's law.

Key term — current: The rate of flow of electric charge, measured in amperes (A).

Worked example: Current and Charge

A current of 0.5 A flows for 20 s. How much charge passes?

0.5 × 20 = 10 C.

Answer: 0.5 × 20 = 10 C.

Common mistakes
  • Connecting a voltmeter in series Voltmeters connect in parallel across the component — in series they would block the current.
  • Saying current is 'used up' in a circuit Current is the same all round a series loop; it is energy that is transferred to the components.

Practice

Two 6 Ω resistors are in series across a 12 V battery. What is the current?
Add the resistances first.

Total R = 12 Ω, so I = 12 ÷ 12 = 1 A.

A bulb has 2 A through it and 12 V across it. Calculate its resistance.
R = V ÷ I.

12 ÷ 2 = 6 Ω.

Why does one blown bulb not darken the other bulbs in a house?
How are houses wired?

House circuits are parallel, so each bulb has its own independent path to the full voltage.

A kettle draws 5 A from the 230 V mains. Calculate its power.
P = IV.

5 × 230 = 1150 W.

Quick check

Current and Charge — quick check

Which of these best defines "current"?

The rate of flow of electric charge, measured in amperes (A).

How much energy does a 100 W bulb transfer in 60 s?

100 × 60 = 6000 J.
Key takeaways
  • Current and Charge: linking current to the flow of charge with Q = I × t.
  • Current is moving charge: In metals, current is a flow of electrons.
  • voltage: The energy transferred per unit charge, measured in volts (V) — the 'push' driving the current.
  • Watch out for: connecting a voltmeter in series
Voltage and Resistance →Back to Grade 11 chaptersRelated resources →