Current (Edexcel GCSE Physics)

Revision Note

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Current & Charge

  • Electric current is defined as the rate of flow charge
    • In other words, the size of an electric current is the amount of charge passing through a component per second

  • The current, charge and time are related by the equation:

  • Where:
    • I = current, measured in amperes (or amps, A)
    • Q = charge, measured in coulombs (C)
    • t = time, measured in seconds (s)

  • The equation for current can be rearranged using the formula triangle below:

Current charge time triangle, IGCSE & GCSE Physics revision notes

Charge, current, time formula triangle

  • The wires in an electric circuit are made of metal, because metal is a good conductor of electric current
  • In the wires, the current is a flow of electrons

electrons-and-current, IGCSE & GCSE Physics revision notes

In metal wires, the current is a flow of electrons. This image shows the electrons flowing through a lattice of metal ions

Worked example

When will 8 mA of current pass through an electrical circuit?

A.     When 1 J of energy is used by 1 C of charge

B.     When a charge of 4 C passes in 500 s

C.     When a charge of 8 C passes in 100 s

D.     When a charge of 1 C passes in 8 s

ANSWER:   B

Step 1: Write out the equation relating current, charge and time

Step 2: Rule out any obviously incorrect options

    • Option A does not mention time, so can be ruled out

Step 3: Try the rest of the options by applying the equation to determine the correct answer

    • Consider option B:

I = 4 ÷ 500 = 8 × 10–3 = 8 mA

    • Consider option C:

I = 8 ÷ 100 = 80 × 10–3 = 80 mA

    • Consider option D:

I = 1 ÷ 8 = 125 × 10–3 = 125 mA

    • Therefore, the correct answer is B

Examiner Tip

Electric currents in everyday circuits tend to be quite small, so it's really common for examiners to throw in a unit prefix like 'm' next to quantities of current, e.g. 10 mA (10 milliamperes). Make sure that you are on the lookout for these prefixes and that you can convert them into standard units, so 10 mA = 10 × 10-3 A.

Ammeters

  • The amount of current flowing through a component is measured using an ammeter
  • Ammeters should always be connected in series with the part of the circuit you wish to measure the current through

Ammeter in series, downloadable AS & A Level Physics revision notes

An ammeter can be used to measure the current around a circuit and always connected in series

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Ashika

Author: Ashika

Expertise: Physics Project Lead

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.