CHAPTER 7 : ELECTRICITY 7.1 : Electrostatics �7.2 : Electricity�7.3 : Measuring Electricity�7.4 : Ohm’s Law �7.5 : Concept of Series & Parallel �

Circuit �7.6 : Current, Voltage & Resistance in �

a Series Circuit �7.7 : Current, Voltage & Resistance in a �

Parallel Circuit �7.8 : Magnestism �7.9 : Electromagnetism�Prepared  by  Ms  Sue  Soh  Ya  Lee  

7.1 : Electrostatics Structure of an ATOM

•  Atom : the smallest particle in an element

•  Has nucleus (proton + neutron) and electrons

•  Different elements have different number of electrons, protons and neutrons in their atoms

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7.1 : Electrostatics Producing Static Electrical Charges

•  Electrostatic : The study of static electrical charges (+ve & -ve)

•  When 2 objects are vigorously rubbed against each other, 1 object receives electrons & the other loses electrons

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7.1 : Electrostatics Producing Static Electrical Charges

•  A charged object attracts uncharged objects

•  Objects with like charges repel each other

•  Objects with unlike charges attract each other

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7.1 : Electrostatics Producing Static Electrical Charges

•  Electroscope : To detect static electrical charges

•  Gold leaf of an uncharged electroscope diverges when a charged object is brought near its metal cap

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7.1 : Electrostatics Everyday Phenomena Related to Static

Electrical Charges •  Lightning : – Due to static electrical charges in the

thunderclouds escaping from cloud to cloud/ a cloud to the earth producing bright flashes

– Friction between water molecules in the clouds & the air molecules produces a large quantity of electrical charges in the clouds

– Lightning is produced when the electrical charges in the clouds escape & produces bright flashes of light & loud sounds of thunder

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7.1 : Electrostatics

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7.1 : Electrostatics Everyday Phenomena Related to Static

Electrical Charges •  Lorry carrying petrol storage tank : – Lorry petrol tanker is in danger of

catching fire because petrol flammable – As the lorry moves along a road, friction

between the lorry & air produces electrical charges on the lorry

– But the rubber tyres of the lorry prevent the charges from escaping to the earth

– A metal chain attached to the lorry touches the road so that electrical charges are conducted by the metal chain to the ground

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7.1 : Electrostatics Everyday Phenomena Related to Static

Electrical Charges •  Car spark plugs : – Car spark plugs

are use to ignite the petrol vapour in the car engine

– When the car engine starts, static electrical charges jump across the gap at the end of the spark plug, producing sparks to ignite the fuel in the engine

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7.1 : Electrostatics Everyday Phenomena Related to Static

Electrical Charges •  Aeroplane : – Aeroplane flying

through the air builds up static electrical charge on its body due to friction with the air

– When aeroplane lands, its special conductive tyres are able to conduct electrical charges to the ground Prepared  by  Ms  Sue  Soh  Ya  Lee  

7.1 : Electrostatics Everyday Phenomena Related to Static

Electrical Charges •  Photostat machine : – Rolling cylinder

in the machine becomes charged with static electrical charges & the paper rolls out is also charged

– Charge paper attracts carbon powder to it to produce a copy of the original document Prepared  by  Ms  Sue  Soh  Ya  Lee  

7.1 : Electrostatics Everyday Phenomena Related to Static

Electrical Charges •  Dry hair : –  Dry hair stands up

when it is vigorously combed on a dry day

– When the hair is combed, friction between the hair & the comb produces static electrical charges

–  As the hair has like charges, the strands of hair repel one another & stand

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7.1 : Electrostatics Safety measures for Electrical Charges

•  Care must be taken when dealing with electrical charges for they can injure/kill/ damage

•  Examples : –  Tall buildings

installed with lightning conductors to prevent the buildings from being damaged by lightning

–  People living on mountains should not use zinc sheets as they attract lightning

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