Скачать или смотреть Alternating Current | LEC-38 | A2-Level Physics 9702 | Basics to Brilliance | Sir Talha | 17th DEC

Alternating current, or AC, is an electric current that changes direction periodically. Unlike direct current (DC), which flows in one direction only, AC constantly reverses its direction as the charge carriers move back and forth in a circuit.
In the UK and many other countries, the mains electricity supply is alternating current with a frequency of 50 Hz, meaning the current completes 50 full cycles every second.
The variation of AC with time is usually sinusoidal and can be described by the equation:
I = I₀ sin(ωt)
where:
I is the instantaneous current
I₀ is the peak current
ω is the angular frequency (ω = 2πf)
t is time
Because AC is constantly changing, we often use its root mean square (rms) value, which gives the equivalent DC value that would produce the same power. For a sinusoidal waveform:
Iᵣₘₛ = I₀ / √2
Vᵣₘₛ = V₀ / √2
AC is widely used in power transmission because it can be easily stepped up or down using transformers, reducing energy losses in transmission cables.