Thus, there is Joule heating and
dissipation 
of 
electrical 
energy 
when 
an
ac current passes through a resistor The instantaneous power dissipated in the resistor is
2
2
sin2
m
p
i R
i R
ωt
=
=
(7 4)
The average value of p over a cycle is*
2
2
sin2
m
p
i R
i R
ωt
= <
> = <
>
  [7 5(a)]
where the bar over a letter (here, p) denotes its average
value and <