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Flip to reveal answersWhat does it mean that charge is 'quantised'?
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All 11 Flashcards — Quantisation of charge
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Question
What does it mean that charge is 'quantised'?
Answer
Charge only comes in **whole-number multiples** of the elementary charge e — never a fraction of e. It changes in fixed steps.
Question
What is the elementary charge e?
Answer
**e = 1.60 × 10⁻¹⁹ C** — the charge on one proton (+e) or one electron (−e). The smallest 'lump' of charge. Given in the data booklet.
Question
Formula linking charge to the number of electrons?
Answer
$Q = N e$ — total charge = whole number N of elementary charges. Rearranged: $N = \dfrac{Q}{e}$.
Question
How do you find how many electrons make up a charge Q?
Answer
Use **N = Q ÷ e**. The answer must be a **whole number**.
Question
Why must N in Q = N e be a whole number?
Answer
Because you can only add or remove **whole** electrons — charge changes in steps of e, so N is always a whole number.
Question
Why is an object negatively charged?
Answer
It has **gained extra electrons**. (A positively charged object has **lost** electrons.) Each electron carries −e.
Question
What did Millikan's oil-drop experiment show?
Answer
Every measured drop charge was a **whole-number multiple of the same smallest step**, e — the experimental proof that charge is **quantised**.
Question
Is a charge of 2.4 × 10⁻¹⁹ C possible? (e = 1.60 × 10⁻¹⁹ C)
Answer
**No.** N = Q ÷ e = 2.4 × 10⁻¹⁹ ÷ 1.60 × 10⁻¹⁹ = 1.5, not a whole number — so it is not allowed.
Question
A charge is 6.4 × 10⁻¹⁹ C — how many electrons? (e = 1.60 × 10⁻¹⁹ C)
Answer
N = Q ÷ e = 6.4 × 10⁻¹⁹ ÷ 1.60 × 10⁻¹⁹ = **4** electrons.
Question
Is Q = N e given in the data booklet?
Answer
**No** — it is the definition of charge quantisation, so memorise it. But the constant **e = 1.60 × 10⁻¹⁹ C** IS given.
Question
A drop of charge 8e splits into two equal halves — charge on each?
Answer
Each half gets **4e** (8e ÷ 2). Still a whole multiple of e, so allowed.
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Structure of the atom
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