EDEXCEL IGCSE PHYSICS 2-2

Electric ChargeEdexcel IGCSE Physics pages 66 to 73

July 13th 2011

Content applying to Triple Science only is shown in red type on the next slide and is indicated on

subsequent slides by ‘TRIPLE ONLY’

Edexcel IGCSE Specification

Section 2: Electricityd) Electric chargeidentify common materials which are electrical conductors or insulators, including metals and plasticsrecall that insulating materials can be charged by frictionexplain that positive and negative electrostatic charges are produced on materials by the loss and gain of electronsrecall that there are forces of attraction between unlike charges and forces of repulsion between like chargesexplain electrostatic phenomena in terms of the movement of electronsrecall the potential dangers of electrostatic charges, eg when fuelling aircraft and tankersrecall some uses of electrostatic charges, eg in photocopiers and inkjet printers.

Red type: Triple Science Only

Electrical conductors and insulatorsAn electrical conductor is a material through which electric current flows easily. All metals are conductors.

Electrical insulators have a very high resistance to the flow of electric current.

Complete the table below:

copper conductor

rubber insulator

steel conductor

mercury conductor

paper insulator

plastic insulator

diamond insulator

graphite conductor

1

2

3

4

5

6

Electric chargeElectric 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.

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Static and current electricity

Static electricity describes the situation when electric charges remain stationary.

This occurs best with insulators.

An electric current occurs when electric charges are moving from one place to another.

This occurs best with conductors.

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Charging materials using frictionWhen 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.

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Force and chargeWhen a charged object is brought close to an uncharged one the two objects attract each other.

The charged comb attracts the column of

water

Charged balloon attracted to a wall

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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.

This boy’s hair has all the same type of charge!

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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 _________’.

insulatingattract repel

positively charge

stationaryelectrons

WORD SELECTION:

rubbing

insulating

attract

repel

positively

charge

stationary

electrons

rubbing

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Hazards of static electricityThe 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.

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Fuel pipe problemsWhen 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.

fuel pipe connected to earth

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Antistatic floorsIn 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.

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Uses of static electricity: 1. 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.

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2. Ink-jet Printer

Spots of ink are given an electric charge as they leave the ink nozzle.

The deflecting plates cause the drops to hit the right part of the paper.

The charges on the deflecting plates change many times per second so that each drop hits the paper in a different position.

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3. Photocopier

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4. 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.

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Online SimulationsBalloons & 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

Electric ChargeNotes questions from pages 66 to 73

1. Explain how a material can become charged using friction (see pages 66 & 67).

2. Describe a simple experiment to show that like charges repel and unlike charges attract (see page 67).

3. Explain with the aid of diagrams how the following devices make use of static electricity: (a) paint sprayers; (b) ink-jet printers; (c) photocopiers (see pages 70 & 71).

4. Describe some of the problems caused by static electricity (see page 72).

5. Answer the questions on page 73.6. Verify that you can do all of the items listed in the end of

chapter checklist on page 73.

TRIPLE ONLY

Online SimulationsBalloons & 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