Knowledge Organiser: Current and Charge
Key Terms
- Current (I): Rate of flow of charge (A)
- Charge (Q): Amount of electricity that flows (C)
- Coulomb: Unit of charge
- Ammeter: Measures current; in series
- Conventional current: Positive to negative
Key Facts
- 1 A = 1 C per second
- Electrons flow negative to positive
- Conventional current: positive to negative
- Ammeter in series with the circuit
- Current is the same throughout a series circuit
Key Equations
- Q = I × t
- I = Q / t
- t = Q / I
Exam Tips
- Always convert minutes to seconds
- State units: A, C, s
- Ammeter = series; Voltmeter = parallel
- Current is conserved — never "used up"
Common Mistakes
- Not converting time to seconds: Q = I × t requires time in seconds — convert minutes by multiplying by 60
- Saying current is "used up": Current is not consumed — the same current flows into and out of a component; energy is transferred, not charge
- Confusing current and charge: Current (A) is the rate of flow of charge; charge (C) is the total amount transferred — they are different quantities
- Placing ammeter in parallel: Ammeters must be in series with the component — placing them in parallel causes a short circuit
- Confusing conventional and electron flow: Conventional current flows + to −; electrons flow − to + — both descriptions are correct in different contexts
Memory Aid
- For Q = I × t — remember "QUIT":
- Q = I × t — the "QUIck Time" an electron takes to flow (Q charges, I current, t time)
- Conventional current direction — "Positive goes Positive":
- Conventional current always flows out of the Positive terminal and in through the negative. The Positive starts the journey.
- Ammeter in Series — "A is Alone in line":
- The Ammeter goes Along the single path — it's in the series loop, never branching off.