Mr Palmer's AQA GCSE Physics Notes

Static Electricity



Charges






An electrically neutral T-shirt



All objects are filled with positive and negative charges as a result of the atoms that comprise them. (Positive charges come from the protons in the nucleus and negative charges come from the orbiting electrons) If an object has an equal number of positive and negative charges, we say it is electrically neutral.

When two different electrical insulators are rubbed together they can become electrically charged.

The t-shirt passes its negative charges (electrons) onto the balloon due to friction. The t-shirt is now electrically positive because it has more positive charges than negative ones. The balloon is electrically negative because it has more negative charges than positive ones. The amount of negative charge that the balloon gains in equal to the amount of positive charge the t-shirt gain. Objects only become positive by losing negative charges. Positive charges do NOT move.




Friction moves electrons from one object to another




Objects that have the same charge (+ + or - -) will repel each other. Objects that have an opposite charge (+ and -) will attract each other.

The charge on an object can be removed by connecting it to the earth with a conductor, such as a wire. Current is the rate of flow of electrons around a circuit. Charges can flow more easily through conductors such as metals. Charges flow with greater difficulty through insulators.

The larger the charge on an object is, the greater the potential difference (voltage) between that object and Earth. If the charge becomes large enough, a spark will carry some of the charge from the object to the nearest earthed conductor.

Sparks can be dangerous in certain situations. For example the anesthetic used in some operating theaters is explosive if sparked. To reduce the chance of a spark antistatic flooring is used. The pipes that deliver petrol to cars and trucks must also be connected to earth to prevent unwanted sparks.



Charge Formula





  • Q: electrical charge measured in coulombs (C)

  • I: current measured in amperes (A)

  • t: time measured in seconds (s)




    • Run!



    A lightening bolt transfers about 5 coulombs of charge in a quarter of a second. What is the current of a lightning bolt?















    Smoke Precipitator






    1. The waste gases pass by a charged metal grid.

    2. The smoke particles pick up an electrical charge from the grid.

    3. The smoke particles are repelled by the like charge on the grid.

    4. The smoke particles are attracted to the oppositely charged collecting plates.

    5. The smoke particles stick to the plates where they eventually fall into the collection traps.

    6. This processes removes much of the particulate pollution from the air.





    The Photocopier






    1. The original document in placed in the photocopier.

    2. A copy plate is electrically charged.

    3. An image of the page is projected onto a positively charged plate. Where the light strikes the plate it becomes decharged.

    4. A blank piece of paper in pressed against the copy plate to pick up charge in the shape of the document

    5. Toner is then spread across the blank page, and is attracted to the charged sections.

    6. Heat is used to fix the toner to the paper to create the finished copy





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    6. Nuclear Radiation
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