__Heating effect of AC__

The RMS voltage and currents are the “DC equivalents”. We know that
*P = VI*, so, if we plot a graph showing the voltage, current,
and power, we see:

The average p.d and the average
current would be **
zero** but this is not
very useful – energy is obviously being transferred so, to get some
idea of an ‘average’, it is useful to look at the power delivered.

Deriving the equation:

Power:

*P* = *IV* = *I*_{0}V_{0}
= P_{max}

For the peak current:

*I*_{0} = I rms × √2

If *I *= 0, power = 0

The mean power:

*P*_{av}* *= *
P*_{max}* ÷ 2 *

The *root mean square* value of I for
a.c. I_{rms}, is the current (dc) that would give the same
power as the mean (ac) power

*I*_{rms }^{2} = Io^{2}
÷ 2

*I*_{rms } =
Io ÷ √2

Also *V*_{rms} = Vo ÷ √2

e.g. for the mains, V_{0 } = 325 V so V_{rms}
= 230 V

Now go on to Tutorial 1 B about the Oscilloscope.
Press the **Next** button below.