Static Electricity

Introduction

• ‘elektron’ ( Greek )

– amber (hard translucent resin)

• Thales

– rubbed amber with fur/wool

• William Gilbert

– Glass, sealing wax, plastic, nylon

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• Electrics (substances) – Acquires attractive property

• Electrified or charged (rubbed bodies)

• Static Electricity– Charge not allowed to flow

• Electrostatics– Branch of electricity

– Study of properties of bodies electrified due to stationary charge

Introduction

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• Glass

• Plastic

• Ebonite

• Amber

• Nylon

• Hard rubber

Charging by Friction

• Wool

• Fur

• Silk

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Examples

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• Positive

• Negative

Types of Charges

Rubbing of two different non-

conducting objects – movement of

electronsChris Sanandam

1. Skin of cat2. Fur3. Glass4. Cotton5. Silk6. Wood7. Indian rubber8. Resin9. Amber10.Sulphur11.Ebonite

Objects

Glass rubbed with fur

Glass rubbed with silk

+-

+ -

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• Electrically neutral (normal state)

– Protons (+e)

– Electrons (-e)

– Neutrons (no charge)

• Mass of proton = mass of neutrons = mass of a hydrogen atom

• Mass of electron = mass of proton

Atom

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• No. of protons & neutrons are different for different elements

• Protons & neutrons are held by nuclear force

• Normal state

Atom

Hydrogen Helium Lithium

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• Valence electron– Outermost orbit

– Attractive force gets weaker as the distance from nucleus increases

• Free electron – When a solid is formed electrons in outermost

orbit leave their atoms

– Move around freely in the solid

Atom

Bound electrons

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Ions

• Positive ions (Cation)

• Negative ions (Anion)

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Transfer of electrons• Case 1:

– Duster & polythene electrically neutral

– When both are rubbed

– Duster (loses electron) becomes +ve

– Polythene (gains electron) becomes –ve

• Case 2– Duster & cellulose acetate electrically neutral

– When both are rubbed

– Cellulose acetate (loses electron) becomes +ve

– Duster (gains electron) becomes –ve

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Electrostatic Induction

Conservation of ChargeCharge is neither created nor destroyed, but transferred from one body to another Chris Sanandam

Static Electricity

• Electrostatic Induction

– Process

– Opposite charge is induced on the nearer end

– Similar charge is induced on the farther end of an uncharged conductor

• Note: induction occurs readily in conductors & is poor in insulators

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Detecting & Testing of Charges,Sparking & Lightning

Electroscope

• Device

• Detect the presence of charge

• Identify the nature of charge

Types• Pith ball electroscope

• Gold leaf electroscope

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Pith Ball Electroscope

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Gold Leaf Electroscope

Brass Disc (cap)

Insulator plug

Brass Rod (stem)

Gold leaves

Glass bottle

Earth

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Gold Leaf Electroscope-Detection of charge

• By touching• Without touching

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Sparking

• The flow of charge

• Between two charged bodies

• Brought close to each other

• With spark & chit-chit sound

• Due to ionisation of air

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Lightning

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Lightning

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