What is Charge in Physics OCR A-Level?

The elementary charge, denoted e, is the smallest unit of electric charge that can exist freely. Its value is approximately 1.6 × 10⁻¹⁹ C. This is the magnitude of charge on a single proton (positive) or a single electron (negative). An electron has charge −e = −1.6 × 10⁻¹⁹ C, while a proton has charge +e = +1.6 × 10⁻¹⁹ C. The elementary charge is a fundamental constant and is used to calculate the charge on ions or charged objects by multiplying by the number of excess or deficit electrons.

What mistakes do students make with Charge?

Using the wrong sign for electron charge. Include the negative sign when calculating net charge due to electrons. Forgetting the exponent: writing 1.6 × 10⁻¹⁹ C as 1.6 × 10¹⁹ C. The charge is very small, so the exponent is negative. Confusing e with the base of natural logarithms. Context determines meaning; in electricity, e is elementary charge.

What are the exam tips for Charge in Physics OCR A-Level?

Memorise the value 1.6 × 10⁻¹⁹ C and its sign for electrons and protons. When calculating net charge, multiply the number of excess electrons by −e, or number of deficit electrons by +e. Check that your answer is a multiple of e; if not, you may have made an error.

OCR · A-Level · Physics

Course version: H556 · Version from Sept 2015

Charge: (c) the elementary charge e equals 1.6 × 10 –19 C

The elementary charge, denoted e, is the smallest unit of electric charge that can exist freely.

Checked against the OCR H556 specification (opens in a new tab) on 10 November 2026.

Point 3 of 7
2 key terms

Study notes

From the checked teaching notes for this specification point.

The idea

For example: An electron has charge −e = −1.6 × 10⁻¹⁹ C, while a proton has charge +e = +1.6 × 10⁻¹⁹ C. The elementary charge is a fundamental constant and is used to calculate the charge on ions or charged objects by multiplying by the number of excess or deficit electrons.

What earns the marks

The elementary charge e = 1.6 × 10⁻¹⁹ C.
Proton charge = +e, electron charge = −e.
Net charge on an object is an integer multiple of e.
Use e to calculate charge from number of particles: Q = n e.

Common mistakes and how to put them right

Using the wrong sign for electron charge.
Put it right: Include the negative sign when calculating net charge due to electrons.
Forgetting the exponent: writing 1.6 × 10⁻¹⁹ C as 1.6 × 10¹⁹ C.
Put it right: The charge is very small, so the exponent is negative.
Confusing e with the base of natural logarithms.
Put it right: Context determines meaning; in electricity, e is elementary charge.

Exam tips

Memorise the value 1.6 × 10⁻¹⁹ C and its sign for electrons and protons.
When calculating net charge, multiply the number of excess electrons by −e, or number of deficit electrons by +e.
Check that your answer is a multiple of e; if not, you may have made an error.

Try the lesson

The start of the Charge: (c) the elementary charge e equals 1.6 × 10 –19 C lesson, made from checked teaching notes for this specification point.

Listen

The elementary charge, denoted e, is the smallest unit of electric charge that can exist freely. Its value is approximately 1.6 × 10⁻¹⁹ C. This is the magnitude of charge on a single proton (positive) or a single electron (negative). For example, an electron has charge −e = −1.6 × 10⁻¹⁹ C, while a proton has charge +e = +1.6 × 10⁻¹⁹ C. The elementary charge is a fundamental constant and is used to calculate the charge on ions or charged objects by multiplying by the number of excess or deficit electrons. A strong answer earns marks for these points. The elementary charge e = 1.6 × 10⁻¹⁹ C. Proton charge = +e, electron charge = −e. Net charge on an object is an integer multiple of e. Use e to calculate charge from number of particles: Q = n e. A common slip: Using the wrong sign for electron charge: electron charge is negative. Instead, include the negative sign when calculating net charge due to electrons. Exam tip: Memorise the value 1.6 × 10⁻¹⁹ C and its sign for electrons and protons.

See it

A flowchart starting from a top node labelled 'Elementary charge e = 1.6 × 10⁻¹⁹ C'. Two arrows lead from it: one to a node labelled 'Proton charge = +e' and one to a node labelled 'Electron charge = −e'. Both of these nodes lead to a node labelled 'Net charge is an integer multiple of e', which leads to a final node labelled 'Q = n e'. — It shows that the elementary charge e gives the proton charge +e and the electron charge −e, and that net charge is an integer multiple of e calculated with Q = n e.

Key words

Say what each word means before you turn the card.

Elementary charge

Try answering aloud or in your head before turning the card.

Calculations involving e

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See every definition

Elementary charge: Equals 1.6 × 10⁻¹⁹ C and is the smallest unit of electric charge that can exist freely.
Calculations involving e: The charge on ions or charged objects is calculated by multiplying e by the number of excess or deficit electrons.

Label the diagram

Some boxes have lost their names. Pick the right name for each number.

The diagram again, with 2 boxes numbered instead of named. A flowchart starting from a top node labelled 'Elementary charge e = 1.6 × 10⁻¹⁹ C'. Two arrows lead from it: one to a node labelled 'Proton charge = +e' and one to a node labelled 'Electron charge = −e'. Both of these nodes lead to a node labelled 'Net charge is an integer multiple of e', which leads to a final node labelled 'Q = n e'.

1Box 1
2Box 2

0 of 2 labelled

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