## Resistance

Ohm's Law for a resistance R in ohms is the linear relationship i=

where v in volts and i in amperes are the instantaneous values of voltage and current. Figure A.4 shows a plot of the applied voltage v = V sin œt

and the resulting current i in a circuit consisting of an AC source and a resistor R. From Equation (A.3) the resulting current is given by

Equation (A.1) shows that the instantaneous power is given by

where V is the RMS value of the AC voltage.

Equation (A.6) is plotted in Figure A.5 i This is a double frequency waveform of average value V2/R and is fully displaced above the time axis. This confirms the evident fact that the power converted in the resistor from electrical into heat form is not dependent on the Time

Figure A.4 Resistor excited by AC voltage

Time v

Figure A.4 Resistor excited by AC voltage v v

### Figure A.5

Power in a resistive component direction of current. It is concluded that to calculate the power in a purely resistive element any of the following expressions can be used: 