Electric Current and Charge

• newEditor
• Physics
• Upper Secondary (Key Stage 4)
• GCSE

Electric Charge and Current

This GCSE physics lesson explores Electric Current and Charge. Students explain current as the rate of flow of charge, use the charge equation and apply current rules to components and complete circuits. It supports KS4 classroom teaching, independent study and exam revision using clear, subject-specific vocabulary.

Current, KS4 Physics, GCSE Physics, Electric Current, Charge, Flow of Electrons, Amperes, Ammeter, Direct Current, Alternating Current, Charge Flow Formula, $Q = It$, Electrical Circuits, MCQs, Open Questions, Polls, Emoji Polls, Exit Tickets

Learning goal

I can explain the relationship between electric charge and electric current, and use I = Q/t to calculate current, charge or time in simple circuits.

What are some words that you think best describe electricity and currents

Use this to surface prior ideas such as electricity, flow, wires, battery, electrons, danger, charge or speed. Briefly note misconceptions to revisit later, especially if students treat current and charge as the same thing.

Electric charge

• Electric charge is a property carried by particles

• In metal wires, the moving charged particles are electrons

• When charge moves through a circuit, energy can be transferred

• The unit of charge is the coulomb (C)

Keep this at GCSE level: students do not need a detailed particle model beyond electrons moving in metal wires.

Current is flow of charge

Electric current is the rate of flow of charge.

A bigger current means more charge passes a point in the circuit each second.

Emphasise 'rate' clearly. Students often say current is just charge; the key idea is charge per second.

How charge flows in a circuit

• Charge flows only when there is a closed circuit

• In an open circuit, charge cannot complete the path

• In a closed circuit, charge moves all the way round the loop

• Current is the same at every point in a single loop circuit

You can link this to a simple series circuit with a cell, lamp and switch. Avoid deeper treatment of branch currents here; the focus is the closed loop idea.

Closed and open circuits

• Closed switch: charge can flow, so there is current

• Open switch: path is broken, so current stops

This slide gives a concrete example of the previous idea. Reinforce that the switch controls whether the path is complete.

Units of current and time

• Current is measured in amperes (A), often called amps

• Time is measured in seconds (s)

• 1 ampere means 1 coulomb of charge flows each second

This prepares the meaning of the equation before showing it formally.

What does electric current describe?

A

flow of energy

B

rate of charge flow

C

amount of voltage

D

movement of atoms

Checks the key distinction from slides 2–6: charge is what moves, current is how much charge passes each second.

Charge, current and units

Electric charge is carried by particles. In metal wires, moving electrons carry charge. Current is the rate of flow of charge, and it is measured in amperes. A closed circuit lets charge flow round the loop.

charge

electrons

amperes

loop

coulombs

seconds

protons

switch

Echoes the wording of slides 2–6 and forces the key terms into distinct positions.

Conventional current and electrons

• Conventional current is defined as flowing from positive to negative

• In metal wires, electrons move from negative to positive

• These directions are opposite

• Circuit diagrams and equations use conventional current

Students often find this odd. Explain that current direction was defined before electrons were discovered, and the convention is still used.

Do not confuse current and p.d.

• Current is the flow of charge

• Potential difference is the energy transferred per unit charge

• Current tells us how much charge flows each second

• Potential difference tells us how much energy each coulomb transfers

Keep this distinction basic. Do not drift into resistance unless needed briefly to avoid confusion.

The current equation

I = Q/t

• I = current in amperes (A)

• Q = charge in coulombs (C)

• t = time in seconds (s)

Stress symbol meanings carefully, especially Q for charge. Students may expect C to be used as the symbol because it is the unit.

What the equation means

The equation shows that current depends on how much charge passes in a given time.

• More charge in the same time → larger current

• Same charge in more time → smaller current

Use everyday language like 'more charge each second means a bigger current' to build intuition before calculation practice.

Rearranging the equation

• To find charge: Q = I × t

• To find time: t = Q / I

• Always check that units are A, C and s

Link these forms directly to the learning goal: students should be able to calculate any one of the three quantities when given the other two.

In metal wires, electrons move from

A

positive to negative

B

negative to positive

C

top to bottom

D

centre to edge

Checks the contrast in slide 7. Students may confuse electron movement with conventional current direction.

Which statement is correct?

A

Current is energy per charge

B

Potential difference is charge per second

C

Current is charge per second

D

Potential difference is current in a wire

Tests the basic distinction between current and potential difference from slide 8, while linking current to charge per second from slides 9–11.

Using I = Q/t

The equation I = Q/t links current, charge and time. In this equation, Q means charge in coulombs, and t means time in seconds. To find charge, you can use Q = I × t.

I = Q/t

Q

t

Q = I × t

I = t/Q

C

A

t = I/Q

Reinforces symbol meaning and one rearrangement after the equation block.

Example: finding current

If 12 C of charge pass through a wire in 3 s:

I = Q/t = 12/3 = 4 A

Model the substitution clearly and include units at each step if you want to slow it down for the class.

Example: finding charge

If a current of 2 A flows for 5 s:

Q = I × t = 2 × 5 = 10 C

Example: finding time

If 18 C of charge pass through a component with a current of 3 A:

t = Q / I = 18 / 3 = 6 s

Point out that the unit for time must be seconds when using these forms at this level.

Measuring current

• Current is measured with an ammeter

• The ammeter is connected in series with the component

• This lets the same current flow through the ammeter

Do not say an ammeter is placed 'across' a component; that would confuse it with a voltmeter.

Why an ammeter is in series

To measure current in a component, the ammeter must be part of the same path as the moving charge.

If it is in series, the charge passing through the component also passes through the ammeter.

This slide gives the reasoning, not just the rule. That helps prevent memorisation without understanding.

A current of 3 A flows for 4 s. What charge is transferred?

A

12 C

B

7 C

C

1.3 C

D

0.75 C

Application of Q = I × t after the worked examples. Distractors reflect adding numbers, decimal confusion, or dividing instead of multiplying.

Why must an ammeter be connected in series?

A

It increases the current

B

It stores charge safely

C

It measures potential difference

D

Same charge passes through it

Targets the reasoning in slides 15–16, not just the rule word 'series'.

How confident do you feel about explaining what electric current is?

Summary

• Charge is measured in coulombs (C)

• Current is the rate of flow of charge and is measured in amperes (A)

• Charge flows only in a closed circuit

• Conventional current is opposite to electron movement in metal wires

• I = Q/t links current, charge and time

• Current is measured with an ammeter in series

Use this to tie back to the central distinction: charge is what flows; current tells us how fast it flows.

Glossary

charge - a property carried by particles that can move through a circuit

current - the rate of flow of electric charge

coulomb (C) - the unit of electric charge

ampere (A) - the unit of current; 1 ampere means 1 coulomb per second

second (s) - the unit of time

closed circuit - a complete path that allows charge to flow

ammeter - a meter used to measure current

Glossary

conventional current - the agreed direction of current from positive to negative

electron - a negatively charged particle that moves through metal wires

potential difference - the energy transferred per unit charge

series - components connected in a single loop so the same current flows through them

I = Q/t - the equation linking current, charge and time