the flow of electricity through wires and cables from the main supply can be compared with the flow of water through pipes from a water tank.

　　when the tap is turned off, the water does not move, but when a tap is turned on the height of the water in the tank exerts pressure on the water in the pipes and forces it through the outlet. this water pressure is comparable with voltage in electricity. the rate of the water flow, similar to the flow of current, is controlled by two things: the pressure and the size of the outlet. for example, a very narrow spray allows less wager to flow than a wide pipe. similarly in electricity, a very thin wire restricts or resists the flow of current.

　　electricians measure this resistance in ohms and the flow of the current in amperes

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