四级英语作文：电流和水流-the flow of electricity and water.doc

文档介绍：The Flow of Electricity and Water
      The flow of electricity through wires and cables from the main supply can pared 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 parable 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 (amps).
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