Current, charge and potential difference
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Question
Define electric current.
Answer
The **rate of flow of charge** — the charge passing a point each second. Unit: ampere (A).
Question
Define potential difference (voltage).
Answer
The **energy given to each coulomb of charge** as it passes through a component. Unit: volt (V).
Question
What is the unit of charge?
Answer
The **coulomb (C)**.
Question
What is the unit of current?
Answer
The **ampere (A)** — one ampere is one coulomb of charge per second.
Question
Formula for current?
Answer
$I = \dfrac{\Delta q}{\Delta t}$ — charge ÷ time. **Given** in the data booklet.
Question
Formula for potential difference?
Answer
$V = \dfrac{W}{q}$ — energy ÷ charge. **Given** in the data booklet.
Question
What does 1 volt mean?
Answer
**1 joule of energy given to every 1 coulomb of charge** (1 V = 1 J C⁻¹).
Question
Rearrange I = Δq/Δt to find the charge.
Answer
$\Delta q = I \times \Delta t$ — current × time.
Question
Rearrange V = W/q to find the energy.
Answer
$W = V \times q$ — voltage × charge.
Question
Is current measured through or across a component?
Answer
**Through** it — an ammeter goes in series (in the line).
Question
Is voltage measured through or across a component?
Answer
**Across** it — a voltmeter goes in parallel.
Question
A belt delivers 0.80 C every 5.0 s. What current is that?
Answer
I = Δq/Δt = 0.80 ÷ 5.0 = 0.16 A.
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