Electrical charge and current: current, I, in amperes, A (amp is acceptable for ampere)

The idea

Electric current measures the rate of flow of electric charge around a circuit. The symbol for current is I, and its unit is the ampere, symbol A; in written work 'amp' is also accepted for ampere. One ampere means one coulomb of charge passing a point each second, so a current of 2 A transfers 2 C every second. Current is measured with an ammeter connected in series with the component being investigated, because the same current must pass through the meter and the component. In a series circuit the current is the same at every point, while in parallel branches the current splits and recombines. When calculating, substitute current in amperes into Q = I t, and remember that a current can be direct or alternating but the unit remains the ampere.

What earns the marks

• States that current is the rate of flow of electric charge, measured in amperes (A).
• Uses the correct symbol I for current and the correct unit symbol A, accepting 'amp' for ampere in written answers.
• Explains that an ammeter is connected in series so that the current to be measured passes through it.
• Applies the relationship charge = current × time, using current in amperes, to calculate charge or current.
• Recognises that one ampere equals one coulomb per second, linking the unit to the definition of current.
• Describes current in series and parallel circuits, including that current is the same throughout a series circuit and divides between parallel branches.

Common mistakes and how to put them right

• Writing the unit as 'amps' when the symbol A is required in a calculation answer.

  Put it right: Give the unit as A, or write 'ampere' or 'amp' in words.

• Connecting an ammeter in parallel with a component.

  Put it right: Connect the ammeter in series so the current flows through it.

• Confusing current with charge or with potential difference.

  Put it right: Current is the rate of charge flow in amperes, charge is measured in coulombs and potential difference in volts.

Exam tips

• Check whether the question asks for the quantity, its symbol or its unit, and answer with exactly that.
• In calculations, convert milliamperes to amperes by dividing by 1000 before substituting into Q = I t.
• When describing a circuit, state where the ammeter is placed and why the reading is the current through that component.