AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Power: current, I, in amperes, A (amp is acceptable for ampere)
Electric current, symbol I, is the rate of flow of electric charge, measured in amperes, symbol A; 'amp' is an acceptable word for ampere.
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Electric current, symbol I, is the rate of flow of electric charge, measured in amperes, symbol A; 'amp' is an acceptable word for ampere. One ampere is one coulomb of charge passing a point each second, so I = Q ÷ t. In the power equation P = V I, current must be in amperes before substitution. An ammeter measures current and is connected in series with the component, because the same current must pass through both the meter and the component. In a series circuit the current is the same at every point, while in parallel branches the currents sum to the total current from the supply.
For example: If 30 C of charge passes a point in 10 s, then I = Q ÷ t = 30 C ÷ 10 s = 3 A.
What earns the marks
- State that current is the rate of flow of electric charge, symbol I, measured in amperes, symbol A (or amps).
- Recall that one ampere equals one coulomb per second, linking I = Q ÷ t to the definition.
- Use I = Q ÷ t and P = V I correctly, converting time to seconds and charge to coulombs where needed.
- Describe connecting an ammeter in series with a component so that the current being measured passes through the meter.
- Interpret current values in series and parallel circuits, including that series current is the same throughout and parallel branch currents add to the supply current.
Common mistakes and how to put them right
Connecting an ammeter in parallel with a component.
Put it right: An ammeter is connected in series so the current to be measured flows through it.
Using minutes directly in I = Q ÷ t.
Put it right: Convert time to seconds before dividing, since one ampere is one coulomb per second.
Forgetting to convert milliamperes (mA) to amperes (A) before calculating power or charge.
Put it right: Divide the mA value by 1000 to get amperes.
Exam tips
- Check that current is in amperes before substituting into P = V I, converting milliamperes by dividing by 1000 if necessary.
- Show the rearranged equation, the substitution and the answer with its unit to make each step clear.
Try the lesson
The start of the Power: current, I, in amperes, A (amp is acceptable for ampere) lesson, made from checked teaching notes for this specification point.
Have a go first
A student reads the label on a battery charger and sees that the current flowing through the charger is measured in amperes. What is the correct symbol for the unit ampere?
Listen
Electric current, symbol I, is the rate of flow of electric charge, measured in amperes, symbol A; 'amp' is an acceptable word for ampere. One ampere is one coulomb of charge passing a point each second, so I = Q ÷ t. In the power equation P = V I, current must be in amperes before substitution. An ammeter measures current and is connected in series with the component, because the same current must pass through both the meter and the component. In a series circuit the current is the same at every point, while in parallel branches the currents sum to the total current from the supply. For example, if 30 C of charge passes a point in 10 s, then I = Q ÷ t = 30 C ÷ 10 s = 3 A. A strong answer earns marks for these points. State that current is the rate of flow of electric charge, symbol I, measured in amperes, symbol A (or amps). Recall that one ampere equals one coulomb per second, linking I = Q ÷ t to the definition. Use I = Q ÷ t and P = V I correctly, converting time to seconds and charge to coulombs where needed. Describe connecting an ammeter in series with a component so that the current being measured passes through the meter. A common slip: Connecting an ammeter in parallel with a component. Instead, an ammeter is connected in series so the current to be measured flows through it. Exam tip: Check that current is in amperes before substituting into P = V I, converting milliamperes by dividing by 1000 if necessary.
Key words
Say what each word means before you turn the card.
Current
Try answering aloud or in your head before turning the card.
Ampere
Try answering aloud or in your head before turning the card.
Ammeter
Try answering aloud or in your head before turning the card.
See every definition
- Current
- The rate of flow of electric charge, with symbol I, measured in amperes, symbol A, where amp is acceptable for ampere.
- Ampere
- One coulomb of charge passing a point each second, so that I = Q ÷ t.
- Ammeter
- A meter that measures current and is connected in series with the component, because the same current must pass through both.
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