Starter activity: think, pair, share 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?
Electrostatics 26/4/13 LO: 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)
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.
Rubbing the rod with a cloth will transfer some of the electrons from the rod to the cloth. B The rod now has fewer electrons than it originally had. This means it has more positive charges than negative. C An uncharged rod will have an equal number of positive and negative charges on it. D The cloth now has more electrons than it originally had and so it is negatively charged. E The rod is now positively charged and can attract uncharged objects like small pieces of paper.
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
Key Points: Electrostatic is caused by the transfer of electrons Insulators can be charged by Friction (or direct contact), which transfers electrons The insulator which gains electrons becomes negatively charged, and the insulator which loses electrons becomes positively charged.
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
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
How does it work ? Two large paddles are charged and placed over the chest – heart region http://commons.wikimedia.org/wiki/File:Defibrillator_Monitor.jpg
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”)
Dust precipitators Electrostatic dust precipitators are used to remove smoke / dust (ash) particles from chimneys http://commons.wikimedia.org/wiki/File:Smoke_plume_from_chimney_of_power_plant.jpg
Paint spraying Static electricity can be useful for paint spraying
Paint Spraying Friction between nozzle and paint droplet causes the droplet to become negatively charged -’ve Metal
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 attracted to oppositely charged positive metal. Droplets repel each other giving an even coat, so there is no wasted paint.
Dust precipitators Metal plates and a grid (or rods) areput into 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 the plates because unlike charges attract. At intervals the plates are vibrated and the dust falls down to a collector.
Prevents charge from building up. Any charge is conducted away 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? Electrons transfer from comb onto her hair Comb loses electrons = positive charge; hair gains electrons = negative charge 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
Would go together in large drops Review 4) A defibrillator is used to restart a patient’s heart. Gel is 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 not charged? 7) What are the advantages of using this method of spraying cars? To give a good electrical contact/reduce contact resistance Causes them to repel Would go together in large drops Even coat / less waste