AQA GCSE Physics 2-4 Static Electricity

AQA GCSE Physics 2-4Static Electricity GCSE Physics pages 160 to 169 July, 2010

AQA GCSE Specification STATIC ELECTRICITY 12.5 What is static electricity, how can it be used and what is the connection between static electricity and electric currents? Using skills, knowledge and understanding of how science works: • to explain why static electricity is dangerous in some situations and how precautions can be taken to ensure that the electrostatic charge is discharged safely • to explain how static electricity can be useful. Skills, knowledge and understanding of how science works set in the context of: • When certain insulating materials are rubbed against each other they become electrically charged. Negatively charged electrons are rubbed off one material onto the other. • The material that gains electrons becomes negatively charged. The material that loses electrons is left with an equal positive charge. • When two electrically charged bodies are brought together they exert a force on each other. • Two bodies that carry the same type of charge repel. Two bodies that carry different types of charge attract. • Electrical charges can move easily through some substances, eg metals. • The rate of flow of electrical charge is called the current. • A charged body can be discharged by connecting it to earth with a conductor. Charge then flows through the conductor. • The greater the charge on an isolated body the greater the potential difference between the body and earth. If the potential difference becomes high enough a spark may jump across the gap between the body and any earthed conductor which is brought near it. • Electrostatic charges can be useful, for example in photocopiers and smoke precipitators and the basic operation of these devices.

Electric charge Electric charge can be either positive or negative. In an atom an electron has a negative charge that is of the same size as the positive charge of a proton. Neutrons have no electric charge. As an atom has the same number of electrons as protons it is uncharged.

Static and current electricity Static electricity describes the situation when electric charges remain stationary. This occurs best with insulators, for example plastic. An electric current occurs when electric charges are moving from one place to another. This occurs best with conductors, for example a metal.

Charging materials When certain insulating materials are rubbed against each other they become electrically charged. Electrons are rubbed off one material onto the other. The material that gains electrons becomes negatively charged. The material that loses electrons is left with an equal positive charge.

The charged comb attracts the column of water Charged balloon attracted to a wall Force and charge When a charged object is brought close to an uncharged one the two objects attract each other.

This boy’s hair has all the same type of charge! Attraction and repulsion Two bodies that carry different types of charge attract. Two bodies that carry the same type of charge repel. The law of charges: LIKE CHARGES REPEL, UNLIKE ATTRACT.

Choose appropriate words to fill in the gaps below: Static electricity occurs when electric ________ remains ____________ on an object. An __________ object can be charged by __________ it with another insulator. One of them gains ________ and becomes negatively charged. The other becomes equally __________ charged. The law of charges states that; ‘like charges _______, unlike _________’. charge stationary insulating rubbing electrons positively repel attract WORD SELECTION: attract insulating electrons repel stationary rubbing positively charge

Electrical chargesNotes questions from pages 160 & 161 • Give two examples of static electricity. • Explain how atoms may become charged. • Draw diagrams and explain how polythene and perspex rods can become charged by friction. • With the aid of a diagram describe an experiment to show that like charges repel and unlike charges attract. • Copy and answer questions (b) and (c) on page 161. • Copy the Key Points on page 161. • Answer the summary questions on page 161.

In text questions: (b) It loses electrons (c) The electron is negative. The nucleus is positive. So there is a force of electrostatic attraction between them Summary questions: (a) gains, to, from (b) loses, from, to (a) attraction (b) attraction (c) repulsion Electrical charges ANSWERS

The arrow shows the direction of electron flow. Electric current An electric current is equal to the rate of flow of electrical charge through a conductor. In metallic conductors (e.g. copper wire) electrons carry negative charge from the negative side of a power supply, around a circuit and back into the positive side.

insulator ground / earth Discharging an object negatively charged object object discharged A charged body can be discharged by connecting it to the ground with a conductor. Charge then flows through the conductor. This process is also called ‘earthing’. A person is usually a good enough conductor to enable an object to be discharged. negative charge flows to earth

lightning is a large spark Sparks The greater the charge on an isolated body the greater the potential difference (voltage) between the body and earth. If the potential difference becomes high enough a spark may jump across the gap between the body and any earthed conductor which is brought near it.

Choose appropriate words to fill in the gaps below: The greater the _______ on an object the greater is the potential difference (or _________) between the object and the earth. An electric current will flow when a ________ is used to link a charged object and the ______. This is called ‘earthing’ and results in the object becoming ___________. Electric current is the rate of _____ of electric charge. If the potential difference is high enough a ____ may occur between the object and the earth. _______ is an example of this. charge voltage conductor earth discharged flow spark lightning WORD SELECTION: voltage conductor discharged spark lightning earth charge flow

Charge on the moveNotes questions from pages 162 & 163 • What does electric current consist of? • Explain, in terms of electrons, how a metal conducts electricity. • Copy and answer question (a) on page 162. • Explain how a conductor can become (a) charged and (b) discharged. • Copy and answer questions (b) and (c) on pages 162 and 163. • When do sparks occur? • Copy the Key Points on page 163. • Answer the summary questions on page 163.

In text questions: The positive end electrons transferred to the can pass through it to the ground. It gains electrons Summary questions: 1. (a) The rate of flow of charge (b) Electrons that move about freely (c) Negatively charged 2. (a) Any charge supplied to it flows to Earth. (b) Charge leaks off the dome form the tip of the pin into the air. Charge on the move ANSWERS

Uses of static electricity: 1. Photocopier

2. Smoke precipitator An electrostatic precipitator is used to prevent the dust and ash produced by coal fired power stations from entering the atmosphere. The ash and dust becomes charged as it passes through the charged grid of wires. The ash and dust is then attracted to the oppositely charged metal plates. When the plates are shaken the accumulated ash and dust falls down to be collected and removed.

3. Paint spraying The spray nozzle is connected is connected to the positive terminal of an electrostatic generator. As the paint droplets leave they repel each other and spread out to form a fine cloud of paint. The metal panel to be painted is connected to the negative terminal. The negatively charged metal panel attracts the positively charged paint.

Hazards of static electricity The main danger of static electricity is in situations where a spark can cause a fire or an explosion. The Buncefield oil depot explosion (opposite) in December 2005 was thought to have been caused by a spark.

fuel pipe connected to earth Pipe problems When oil or petrol is pumped along pipes a static charge can build up on the pipe which could result in a spark. This could cause an explosion when the fuel vapour reacts with oxygen in the air.

Antistatic floors In operating theatres it is important that the doctors to do not become statically charged when walking around. This is because some of the anaesthetic gases used are explosive. Antistatic material is used for the floor surface so that any charge is conducted to earth.

Uses and dangers of static electricityNotes questions from pages 164 & 165 • Explain how static electricity is used in: (a) a paint sprayer and (b) an electrostatic precipitator (draw a diagram) • Copy and answer questions (a), (b) and (c) on page 164. • Explain three hazards of static electricity. • Copy and answer questions (d) and (e) on page 165. • Copy the Key Points on page 165. • Answer the summary questions on page 165.

In text questions: So that droplets are charged as they leave the spray nozzle and attracted to the panel. Most of the particles would pass straight through it. The powder transfers charge onto the paper from the photocopier drum. The charge stays on the paper sometimes. So that it conducts charge away from the pump nozzle to Earth. So their clothing doesn’t become charged and produce sparks. Summary questions: (a) repelled, gain (b) lose, attracted 2. (a) To conduct any charge on the pipe nozzle to the ground, so it can’t cause sparks which would ignite the fuel. (b) To conduct any charge to the ground so it can’t cause sparks, which would cause gases used in the theatre to explode. Uses and dangers of static electricityANSWERS

Electrometer.exe – Electroscope Electrostatic Induction.exe – Does not work in all cases Electrostatic Pendulum.exe - Shows how current is produced by charge flow Van der Graaf.exe Virtual Physics Laboratory SimulationsNOTE: Links work only in school

Balloons & Static Electricity - PhET - Why does a balloon stick to your sweater? Rub a balloon on a sweater, then let go of the balloon and it flies over and sticks to the sweater. View the charges in the sweater, balloons, and the wall. Electric & Magnetic Forces - 'Whys Guy' Video Clip (3:30mins) - Shows Charged Balloon & Effect of a magnet on a TV screen. John Travoltage - PhET - Make sparks fly with John Travoltage. Wiggle Johnnie's foot and he picks up charges from the carpet. Bring his hand close to the door knob and get rid of the excess charge. Fuel Ignition While Refuelling A Car - Word document with embedded video clip Charged Rod & Pith Ball - Iona Electric Force Tutorial - Science Trek How photocopying works - University of Delaware BBC KS3 Bitesize Revision: Electrical Charge BBC AQA GCSE Bitesize Revision: Attraction & Repulsion Uses of static electricity Charge, current, energy and time relationships Online Simulations

Static issuesNotes questions from pages 166 & 167 • Answer questions 1, 2 and 3 on pages 166 and 167.

Static issuesANSWERS 1. (a) All charged objects either attract or repel each other. You only need two types to fit the force rule. (b) All the extra electrons carrying the negative charge would make up for the deficit of electrons in the positive charge. 2. Electrons transfer to the electroscope so the leaf and the stem both become positively charged. The leaf therefore goes up. The charge stays on the electroscope so the leaf stays up. 3. They would not be deflected by the correct amount.

How Science WorksANSWERS • To ensure that the results are valid, i.e. it is a type of control for different people carrying out the testing. • When lightning was striking. • The air temperature. • As many people as possible (e.g. a minimum of 50 as there is likely to be a wide range of temperatures.) • Microseconds are used to time the response of the lightning conductor. • The lightning conductor may have been damaged. • It could be done by both. However, a potential buyer would want to be assured of its reliability and therefore an independent company would be better. The testing will probably be monitored by an independent company.

AQA GCSE Physics 2-4 Static Electricity