P2 Topic 1 – Static and current electricity  Static electricity is caused by an electrical  Generating static electricity: (‘electrostatic’) charge building up on insulating  When two insulating materials are rubbed materials – including on you together, friction is generated and electrons  All atoms contain electrically charged particles may be transferred from one material to the called protons and electrons: other (note: protons can’t be transferred o Protons have a positive charge and are because they are fixed in the nuclei of atoms): found in the nucleus of atoms o The material gaining electrons now o Electrons move around the outside of the has more electrons than atom at different distances from the nucleus protonshas a negative charge – they are negatively charged o The material losing electrons now o The positive charges on the protons are has more protons than balanced by the negative charges on the electronshas an equal positive electronsatoms have no overall charge charge  Note: the nucleus also contains neutrons, which  Objects charged with static electricity can have no charge attract or repel each other: o If the charges on the two objects are  Why it’s difficult to charge a conducting different, they will attract each other material with static electricity: o If the charges are the same as each  Insulating materials (e.g a polythene rod) do not other (i.e both positive or both conduct electricity…: negative), the objects repel o electrons that are transferred cannot move through the material – i.e they stay close together at the end of the polythene rod o static charge builds up at the end of the polythene rod  Conducting materials (e.g a metal rod) conduct electricity…: o electrons that are transferred spread themselves out through the metal rod o the extra static charge is difficult to detect  This is why static electricity builds up between insulating materials and not between conducting materials  If you rub a balloon on a jumper you can get it to stick to a wall – this process is called charging ‘by induction’ and the charge produced is an induced charge…  Explanation for this: o When the balloon is rubbed against the jumper, electrons are transferred from the jumper to the balloonthe balloon becomes negatively charged o When the balloon is placed against the wall, the electrons in the wall are repelled by the balloon’s negative charge and move away

Generating static electricity cont.. The positive charge left behind on the wall (the DANGERS OF STATIC ELECTRICITY ‘induced charge’) attracts the negative charge on the  Shocks from everyday objects: P2 Topic 1 – Static and current electricity balloonthe balloon sticks to the wall  You can sometimes build up an electrostatic charge just by walking on a carpet: o As the shoes rub along the carpet, electrons are transferred from the carpet to the personperson becomes negatively charged o If the person then touches a conducting material (e.g metal object), the person feels a small electric shock as electrons flow from the person, through the metal object to the earth  The process of electrons flowing from a person ______to the ground through an object, or the other _ way around, is called ‘earthing’ USES OF STATIC ELECTRICITY  After earthing, the person is discharged (i.e no  Static electricity can be useful… longer has an electrostatic charge)  E.g it can be used in electrostatic spray painting to make the spray spread out…: o The metal spray nozzle is connected to the positive terminal of an electricity supplydroplets of paint pick up a positive charge o The positively charged droplets repel each otherspread out o The object to be painted is given a negative charge o the paint droplets are attracted to the surface of the object  Lightning:  Note: static electricity is also used in insecticide  Large charges of static electricity can build up sprayers on clouds, causing electrons to flow through the atmosphere between the clouds and the ground (electrons can flow in either direction…i.e from ground to clouds or from clouds to ground)  This produces the huge spark that we see as lightning

 Overcoming the dangers of electrostatic charges:  To reduce the dangers of the build-up of static electricity… o there needs to be a path between the object with electrostatic charge and the ground, through which electrons can flow… . for electrons to flow along it, the ‘path’ must be made of a material that conducts USES OF STATIC ELECTRICITY Cont.. electricity…in most cases, it’s made of metal

DANGERS OF STATIC ELECTRICITY cont.. This earthing process discharges the object and P2 Topic 1 – Static and current electricity prevents sparks being produced  E.g refuelling aircraft: o As fuel flows through a refuelling pipe, static electricity can build up o The aircraft can also build up a static charge as it flies through the air o a bonding line (a metal wire) is used to connect the aircraft to the earth before it is refuelled o This discharges the aircraft of any electrostatic charge that may have built upno sparks are produced  A similar problem can occur when tankers deliver fuel to filling stations: o In this case, the hose used to fill the underground fuel tanks is made of a conducting materialno sparks are ______produced P2 Topic 1 – Static and current electricity  ELECTRIC CURRENTS

 In conducting materials (e.g metals), some of the electrons from each atom are free to move about - this flow of electrons produces an electric current  In a piece of metal, the free electrons all move round in different directions

 When a metal wire is placed in an electrical circuit (it must be a complete circuit), the cell (battery) pushes the free electrons in one direction around the circuit… o Cells and batteries supply current that flows in only one direction – this is called ‘direct current’  Generators produce ‘alternating current’ – i.e electrons change direction many times each second

 Charge and current:  An electric current is the rate of flow of charged particles P2 Topic 1 – Static and current electricity  Units: o Charge – measured in coulombs (C) o Current – measured in amperes (or amps, A)  The size of the electric current depends on how much charge is passing a point in a circuit each second: o 1 ampere is a flow of 1 coulomb of charge per second  The equation linking charge and current: o charge (coulombs, C) = current (amps, A) x time (seconds, s) o Q = I x t o I.e the more charge that passes a point in a circuit per second, the greater the current

 E.g: o a current of 5A flows for 10s…how much charge has flowed through the circuit? o Charge = 5 x 10 = 50 C