The three forms of Ohm's law are I = V/R, V = IR, and R = V/I
One ampere is the amount of current produced by one volt of potential difference across one ohm of resistance. This current of 1 A is the same as 1 C/s.
With R constant, the amount of I increases in direct proportion as V increases. This linear relation between V and I is shown by the graph in Fig. 3–5.
With V constant, the current I decreases as R increases. This is an inverse relation.
Power is the time rate of doing work or using energy. The unit is the watt. One watt equals 1 V x 1 A. Also, watts = joules per second.
The unit of work or energy is the joule. One joule equals 1 W x 1 s.
The most common multiples and submultiples of the practical units are listed in Table 3–1.
Voltage applied across your body can produce a dangerous electric shock. Whenever possible, shut off the power and make resistance tests. If the power must be on, use only one hand when making measurements. Place your other hand behind your back or in your pocket.
Table 3–2 summarizes the practical units of electricity.
An open circuit has no current and infinitely high R. A short circuit has zero resistance and excessively high current.
