2. 外语
  3. Switch开关 An electric switch is often on a wall near the door of a room. / Two wires lead to the lamp in the room. / The swit

Switch开关 An electric switch is often on a wall near the door of a room. / Two wires lead to the lamp in the room. / The swit

admin2016-03-05  19
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答案Switch开关 An electric switch is often on a wall near the door of a room. / Two wires lead to the lamp in the room. / The switch is fixed in one of them. / The switch can cause a break in this wire, and then the light goes. / The switch can also join the two parts of the wire again, then we get a light. / Switch can control many different things. / Small switches control lamps and radio sets because these do not take a large current, / larger switches control electric fires. / Other switches can control electric motors. / Good switches move quickly. They have to stop the current suddenly. / If they move slowly, an electric spark appears. / It jumps across the space between the two ends of the wire. / This is unsafe and it heats the switch. / Very big switches are sometimes placed in oil. / Sparks do not easily jump through oil, so the oil makes the switch safer. /
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