In an a.c circuit the e.m.f. (e) and the current (i) at

In an a.c circuit the e.m.f. (e) and the current (i) at any instant are given respectively by
e = E₀ sin ωt
i = I₀ sin (ωt – φ)
The average power in the circuit over one cycle of a.c. is

The average power in the circuit over one cycle of a.c. is given by
P^av = e^rms × i^rms × cosφ

=	E₀	.	I₀	. cos f =	E₀ I₀	cos f
	√2		√2		2

	E₀I₀
	2

	E₀I₀	sin φ
	2

	E₀I₀	cos φ
	2