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Electrostatics

Electrostatics. Starter activity: think, pair, share Read the rich questions below, think about possible answers, share your answers with your peer, share your answers with the rest of the class.

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Electrostatics

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  1. Electrostatics Starter activity: think, pair, share Read the rich questions below, think about possible answers, share your answers with your peer, share your answers with the rest of the class. Q) If positive and negative things attract each other, why aren’t electrons found in the nucleus of an atom? Q) Is static really electricity?

  2. Electrostatics 26/4/13LO: to be able to:1) Understand how insulating materials can become charged (grade C)2) Describe how smoke particles, etc are removed from chimneys using charged plates (grade A)3) explain how static electricity is used in paint spraying in terms of electron movement (grade A)

  3. Electrostatics • Electric charge (current) does not flow in an insulator. • However, when two insulators are rubbed together electrons from the atoms on the surface of one insulator are transferred to the surface of the other.

  4. The movement of electrons in this way to form charged objects is known as static electricity or electrostatics: • A positive charge (object) is due to a loss of electrons • A negative charge (object) is due to gaining of electrons. • Like charges repel and opposite charges attract

  5. Key Points: • Electrostatic is caused by the transfer of electrons • Insulators can be charged by Friction (or direct contact), which transferselectrons • The insulator which gainselectrons becomes negatively charged, and the insulator which loseselectrons becomes positively charged.

  6. Forces between static charge • Static charge are held together simply by electrostatic forces of attraction. • This simply means, like charges repel and unlike charges attract

  7. Uses of electrostatics • Static electricity can be useful for restarting the heart when it has stopped (fibrillation) • Paramedics and Doctors use a devise called a defibrillator which uses electrostatics to restart the heart

  8. How does it work ? • Two large paddles are charged and placed over the chest – heart region

  9. Clothes are removed for good electrical contact with patient’s chest • A large charge passes through patient to make heart contract • Care is taken not to shock operator – insulated handles & no contact with patient during surge of charge (“stand clear”)

  10. Dust precipitators • Electrostatic dust precipitators are used to remove smoke / dust (ash) particles from chimneys

  11. Paint spraying • Static electricity can be useful for paint spraying

  12. -’ve Paint Spraying Friction between nozzle and paintdroplet causes the droplet to become negatively charged Metal

  13. Key Points:Paint Spraying • The paint gun is charged (i.e. negative) . • Paint droplets become negatively charged due to friction as they move out of nozzle of spray gun • Like charges repel so the paint particles spread out giving a fine spray • The metal bicycle frame to be painted is oppositely charged (positive) • Opposite charges attract so paint droplets are attractedto oppositely charged positive metal. • Droplets repel each other giving an evencoat, so there is no wasted paint.

  14. Dust precipitators • Metal plates and a grid (or rods) areputinto the chimney. • They are connected to a high-voltage supply so that the grid becomes negatively charged. • The plates are earthed and gain the opposite charge to the grid • As the dust particles pass the grid (or rods) they become negatively charged. • The dust particles are attracted to theplates because unlike charges attract. • At intervals the plates are vibratedand the dust falls down to a collector.

  15. Review 1) Sarah is combing her hair. The comb becomes positively charged. Explain carefully how this happens 2) Spare petrol for cars must always be carried in a metal can. Why is a plastic can dangerous 3) Aircraft tyres are made from a type of rubber that conducts electricity. Why? Plastic is an insulator [1] so charge can build up and cause a spark igniting fuel [1]. Metal is a conductor so any charge is conducted away Prevents charge from building up. Any charge is conducted away Electrons transfer from comb onto her hair Comb loses electrons = positive charge; hair gains electrons = negative charge

  16. Review 4) A defibrillatoris used to restart a patient’s heart. Gelis sometimes put onto the patient’s chest before the paddles are applied. Suggest a reason why. Electrostatics is useful in paint spraying. The spray nozzle is at a high voltage and gives the paint a charge. 5) What effect does this have on the droplets of paint? 6)What would happen if the paint was notcharged? 7) What are the advantagesof using this method of spraying cars? Causes them to repel Would go together in large drops Even coat / less waste To give a good electrical contact/reduce contact resistance

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