OCR · A-Level · Physics
Course version: H556 · Version from Sept 2015
(d) net charge on a particle or an object is quantised and a multiple of e
Full specification wording
Charge: (d) net charge on a particle or an object is quantised and a multiple of e
Quantisation of charge means that the net electric charge on any particle or object can only take discrete values that are integer multiples of the elementary charge e.
Checked against the OCR H556 specification (opens in a new tab) on .
- Point 4 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Quantisation of charge means that the net electric charge on any particle or object can only take discrete values that are integer multiples of the elementary charge e. In other words, charge is not continuous; it comes in 'packets' of size e = 1.6 × 10⁻¹⁹ C. For example, an object can have a charge of +2e, −3e, or zero, but never +1.5e. This arises because charge is carried by discrete particles like electrons and protons. When an object is charged, it gains or loses whole electrons, so its net charge is always an integer multiple of e. Mathematically, Q = n e, where n is an integer (positive, negative, or zero). This principle is fundamental in physics and explains why charge is quantised. In calculations, you can determine the number of excess or deficit electrons by dividing the net charge by e.
What earns the marks
- Net charge on a particle or object is quantised.
- Charge is always an integer multiple of the elementary charge e.
- Q = n e, where n is an integer.
- Quantisation arises because charge is carried by discrete particles (electrons, protons).
- The smallest possible free charge is e (or −e for an electron).
Common mistakes and how to put them right
Thinking charge can be any continuous value.
Put it right: Express charge as n e with integer n.
Forgetting that n can be negative.
Put it right: Include the sign of the charge when determining n.
Confusing quantisation with conservation.
Put it right: These are separate principles.
Exam tips
- When asked if a charge is possible, check if it is an integer multiple of e.
- To find the number of excess electrons, divide the net charge by −e (if negative) or e (if positive).
- Remember that the net charge on an object is the sum of charges of all its constituent particles.
Try the lesson
The start of the Charge: (d) net charge on a particle or an object is quantised and a multiple of e lesson, made from checked teaching notes for this specification point.
Listen
Quantisation of charge means that the net electric charge on any particle or object can only take discrete values that are integer multiples of the elementary charge e. In other words, charge is not continuous; it comes in 'packets' of size e = 1.6 × 10⁻¹⁹ C. For example, an object can have a charge of +2e, −3e, or zero, but never +1.5e. This arises because charge is carried by discrete particles like electrons and protons. When an object is charged, it gains or loses whole electrons, so its net charge is always an integer multiple of e. Mathematically, Q = n e, where n is an integer (positive, negative, or zero). This principle is fundamental in physics and explains why charge is quantised. In calculations, you can determine the number of excess or deficit electrons by dividing the net charge by e. A strong answer earns marks for these points. Net charge on a particle or object is quantised. Charge is always an integer multiple of the elementary charge e. Q = n e, where n is an integer. Quantisation arises because charge is carried by discrete particles (electrons, protons). A common slip: Thinking charge can be any continuous value: charge is quantised, so only multiples of e are possible. Instead, express charge as n e with integer n. Exam tip: When asked if a charge is possible, check if it is an integer multiple of e.
See it
Key words
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Quantisation of charge
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Elementary charge
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Discrete nature of charge
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Calculations with integer multiples of e
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See every definition
- Quantisation of charge
- The net electric charge on any particle or object can only take discrete values that are integer multiples of the elementary charge e.
- Elementary charge
- Charge comes in 'packets' of size e = 1.6 × 10⁻¹⁹ C, and the smallest possible free charge is e (or −e for an electron).
- Discrete nature of charge
- Charge is not continuous; it arises because charge is carried by discrete particles like electrons and protons, so an object gains or loses whole electrons.
- Calculations with integer multiples of e
- Using Q = n e, where n is an integer (positive, negative, or zero), and dividing the net charge by e to determine the number of excess or deficit electrons.
Label the diagram
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1Box 1
2Box 2
3Box 3
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