Electricity

[SMR108]

How is electricity measured?

[Ed Ancona]

An analogy with water in a pipe can help. The amount of water flowing can depend on the diameter of the pipe and the pressure of the flow. Likewise, electricity is measured by the amount of current flowing (ampereres) and the pressure (volts.) there are specialised meters called, naturally, ammeters and voltmeters to measure those factors. A more important measure is the amount of eneregy flowing. How big a waterwheel can the water pipe turn? That is a function of the amount of water and its pressure. Likewise the electrical energy is measured in watts. How big a motor can the connected wire run? A function of the voltage and amperage. Measured by a watt meter. Total energy over a certain time is measured in watt-hours. How much work did the motor do?

[Ed Ancona]

In addition to correcting my typo, amperes, I can point out that the meter outside your house where the electric service enters is a watt-hour meter. It measures tha amount of power (watts) you have used over a certain time (watt-hours.) The electric company charges you for the energy at a certain price per watt-hour. Or in a more convenient form, kilowatt-hours (thousand watt-hours.) The price may be on the order of 5 to 10 pence per kilowatt-hour. Less if you're lucky.

[Sensei]

I'm guessing you mean with a meter. Current passing through a wire causes a magnetic field in proportion to the amount of current flowing. (Coiling the wire concentrates the field.) The needle on a meter is moved by the magnetic field. The more current flowing, the greater the magnetic field, the more the needle moves. There's a little more to it, but that's the basic idea.