Physics

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Charge

If you rub two insulating materials against each other they become electrically charged. This only works for insulators as conductors lose the charge to earth.

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Fill in the gaps!

If you rub two ....................... against each other they become electrically charged. This only works for .................... as ........................ lose the charge to .................

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When materials rub against each other....

What are the four things that happen when materials are rubbed against each other? 

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When materials rub against each other....

 

  • negatively charged particles called electrons move from one material to the other
  • the material that loses electrons becomes positively charged
  • the material that gains electrons becomes negatively charged
  • both materials gain an equal amount of charge, but the charges are opposite
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Discharge

A charged object can be discharged by connecting it to earth with a metal wire or other conductor. If the potential difference (voltage) is very large, a spark may jump across the gap between the charged object and the conductor. This can be dangerous. For example, it could cause an explosion in a petrol station.

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Discharge

What could happen if the potential difrence is very large when discharging a charged object?

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Electrostatic precipitators

Many power stations burn fossil fuels such as coal and oil. Smoke is produced when these fuels burn. Smoke comprises tiny solid particles, such as unreacted carbon, which can damage buildings and cause breathing difficulties. To avoid this, the smoke is removed from waste gases before they pass out of the chimneys. The electrostatic precipitator is the device used for this job.

  1. Smoke particles pick up a negative charge.
  2. Smoke particles are attracted to the collecting plates.
  3. Collecting plates are knocked to remove the smoke particles.
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electrostatic precipitators

(http://www.bbc.co.uk/schools/gcsebitesize/science/images/105_reducing_pollution_v2.gif)

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Photocopiers

1. The image of the document is projected onto a positively charged copying plate. 2. Where light falls onto the plate, the electrical charge leaks way. 3. Negatively charged black toner particles are attracted to the remaining positive areas. 4. Paper is placed over the copying plate: toner is transferred to the paper and heated to make it stick. 5. The photocopy is taken off the copy plate and turned over to reveal the text (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ph_elect27.gif)

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