Alternating current (ac)

Definition

Alternating current (AC) is an electric current that periodically reverses direction. Unlike direct current (DC), AC voltage and current change their magnitudes continuously with time.

5 Must Know Facts For Your Next Test

1. The frequency of AC in most countries is 50 Hz or 60 Hz, depending on the region.
2. AC voltage can be represented mathematically as $V(t) = V_0 \sin(\omega t)$, where $V_0$ is the peak voltage and $\omega$ is the angular frequency.
3. Root Mean Square (RMS) value of AC is used to represent its effective voltage or current: $V_{rms} = \frac{V_0}{\sqrt{2}}$.
4. Transformers are devices used to increase or decrease the voltage of alternating current.
5. AC power can be calculated using the formula $P = V_{rms} I_{rms} \cos(\phi)$, where $\phi$ is the phase difference between voltage and current.

Review Questions

• What is the mathematical representation of AC voltage?
• How do you calculate the RMS value of an alternating current's peak voltage?
• What role do transformers play in alternating-current circuits?

Related terms

Frequency:

The number of cycles per second in an alternating current, measured in Hertz (Hz).

Transformer:

A device used to change the voltage level in an AC circuit by electromagnetic induction.

Root Mean Square (RMS): A statistical measure of the magnitude of a varying quantity, often used to determine the effective value of AC voltage or current.