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Current, potential difference and resistance
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Electric circuits power almost everything around you. Current, potential difference and resistance explain how they work.
Current
Current is the flow of electric charge around a circuit. It is measured in amperes (A), or amps, with an ammeter placed in series.
In a series circuit (one loop), the current is the same everywhere.
In a parallel circuit, the current splits at a junction. The currents in the branches add up to the current from the battery.
In a series circuit (one loop), the current is the same everywhere.
In a parallel circuit, the current splits at a junction. The currents in the branches add up to the current from the battery.
Potential difference
Potential difference (p.d.) is the push that drives the current. It is measured in volts (V) with a voltmeter placed in parallel across a component.
Cells and bulbs are given voltage ratings.
In series, the battery's p.d. is shared between the components. In parallel, each branch gets the full p.d.
Cells and bulbs are given voltage ratings.
In series, the battery's p.d. is shared between the components. In parallel, each branch gets the full p.d.
Resistance
Resistance tells you how hard it is for current to flow. It is measured in ohms (Ω).
resistance = potential difference ÷ current (R = V ÷ I)
Conductors such as copper have a low resistance. Insulators such as plastic have a very high resistance, so almost no current flows.
resistance = potential difference ÷ current (R = V ÷ I)
Conductors such as copper have a low resistance. Insulators such as plastic have a very high resistance, so almost no current flows.
A bulb has a p.d. of 6 V across it and a current of 0.5 A through it. Find its resistance.
- R = V ÷ I
- R = 6 ÷ 0.5
Answer: 12 Ω
Current (A) is the flow of charge: the same everywhere in series, split between branches in parallel. Potential difference (V) is shared in series and the same across parallel branches. Resistance (Ω) = V ÷ I.
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