2.2.4 AC & DC

Direct Current (DC)

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A direct current (DC) is an electric current that constantly flows in only one direction, at a constant voltage. On a graph plotting current or voltage against time for direct current, the line would be horizontal.

Alternating Current (AC)

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An alternating current (AC) is an electric current that reverses direction at regular intervals.

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On a graph plotting current or voltage against time for AC, the values will alternate between positive and negative. This shows the direction that the current flows.

Benefit: Alternating current is used for long-distance energy transmission because it can be transferred more efficiently - It is very easy to use a transformer to increase or decrease the potential difference (P.D.).
Specifications:
- Frequency: 50 Hz
- P.D.: 230V In the UK, the mains electricity supply operates at a frequency of 50 Hz with a potential difference of 230 V. This means the voltage fluctuates between +230 V and -230 V, causing the current to change direction 50 times per second.

Oscilloscope

Function: Used to see the pattern of an electrical current.

infoNote

Formula for Frequency:

\text{frequency} = \frac{1}{t}

Variables:
$t$ : Time of one cycle

Graphs

DC Supply: Current remains constant over time.
AC Supply: Current changes direction periodically over time.

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