# Electricity

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## Static Electricity

When different materials are rubbed together, ELECTRONS move from one material to the other.

Some Materials GAIN electrons while some LOSE electrons.

same charge = Repel                                                           Opposite charges = Attract

Gold Leaf Electroscope has a negative charge and can be used to investigate the charge of another object. Negative objects cause the Gold leaf to rise more and positive less!

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## Electrostatic Induction

Electrostatic Induction is: a negatively charged object sticking to an UNCHARGED object.

It does this because negative charge REPELS electrons from the SURFACE of the UNCHARGED object leaving it with a POSITIVE CHARGE.

Effect of static electricity is greater on dry days than humind days, as moisture in damp air can conduct some charge away from objects.

ELECTROSTATIC DISCHARGE IS DANGEROUS!

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## Ohm's Law

Ohms law is: Voltage is proportional to current, and ressistance is constant!

A wires ressistance is greater if the wire is longer or thinner, this is because electrons are more likely to collide with the nuclei in the material.

For example: A filament bulb does not obey Ohms Law, as current in a filament bulb increases its resisstance increases.

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## How Do some Components Work?

Diodes, LDRs, Thermistors and Light Emmiting Diodes are made from SEMICONDUCTER materials

Electrons Gain enough Energy when material is heated or light shines on it to be able to flow through.

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## P.D & Resistance in Series

Series Circuit

• Current is same in all places
• Each components resistance added together = Total resistance
• Supplied potential energy is shared across compnents
• Components with a high resistance has a larger potential difference than component with small resistance
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## P.D & Resistance in Parallel

Parallel

• Current in paralell circuit has more than one path, it divides at junctions and joins up again.
• Current in each loop depends on total resistance in that loop, Smaller current flows through loops with a high resistance
• Total current leaving and returning to battery is the sum of currents in each loop
• All bulbs stay bright as if one bulb was in parallel circuit.
• P.D across each compnent in parallel circuit is the same
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