Electricity

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IGCSE Physics (P3 Electricity) Note on Electricity, created by ShreyaDas on 04/04/2014.
ShreyaDas
Note by ShreyaDas, updated more than 1 year ago
ShreyaDas
Created by ShreyaDas about 10 years ago
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Definition: a stationary electric charge, typically produced by friction, which causes sparks or crackling or the attraction of dust or hair. Static Electricity is: - concerned with charges that are not moving Like charges repel Unlike charges attract two rubbed polythene strips would repel rubbed cellulose acetate strip (balanced on a watch glass) and rubbed polythene trip would attract Charge on cellulose acetate is positive and charge on polythene is negative There are positive charges and there are negative charges Electrons transfer

Rubbing a polythene rod vigorously with a cloth causes the electrons to move from the cloth to the rod result: negatively charged polythene (excess electrons) positively charged cloth (Electron deficiency)  Rubbing does not create charge - it causes a separation (transfer) of charge (electrons)  only negatively charged electrons are albe to move positive charge cannot move because protons are in the nucleus Electrons carry negative charge  negatively charged object has an excess of electrons positively charged object has a shortage of electrons POSITIVE CHARGES CANNOT MOVE

In an insulator:  - all electrons are bound firmly to their atoms  - can be charged by rubbing because the charge produced cannot move from where the rubbing occurs (electric charge is static) In a conductor:  - some electrons can move freely from atom to atom  

Conductors: Mostly metals The metal atoms contain free moving electrons that are able to carry the current These electrons collide with the metal ions to create a resistance to the electronic flow e.g. steel, iron, silver, copper, aluminium, graphite & silicon Allows an electric current to flow through them The length of a conductor is directly proportional to the resistance e.g. the double the length of the copper wire, the double the resistance However, the resistance is inversely proportional to the cross-section area e.g. The more electrons in the wire, the less resistance. Insulators: Mostly plastics Can be charged with static electricity by using friction Extra electrons are added to the insulating material The electrons stay at the surface of the material and attracts itself to something that ispositively charged When you rub a polyethene rod with a cloth, electrons transfer from the cloth to the rod. Therefore, it gains a negative charge. You can also take away electrons from the material so that it carries a positive charge

Current Electricity: flow of electrons along a wirecell or battery can be used to 'pump' the charge along the wire(currents can produce heat, light, motion)electrons are already in the wire, cell = pump

current is the rate of flow of charge measured in amps potential difference is the amount of energy given out per coulomb of electricity passing through a component emf: energy supplied per unit charge amount of chem --> elect per unit charge resistance is a measure of how much an electrical component opposes current flow charge is measured in coulombs   

I = Q/Tcurrent = charge/time

Voltmeters Used to measure the potential difference across a certain section of a circuit. ALWAYS connected in PARALLEL. Ammeters Used to measure the current in the entire circuit. ALWAYS connected in SERIES. 

Voltage:- amount of potential energy between two points- amount of energy converted per coulomb of electricity passing through a component

Voltage: Energy/ChargeV = E/QVoltage: Current x ResistanceV = IR 

Current: flow of electrons along a wire - rate of flow of charge - charge flowing per second - measured in amperes (coulombs per second) electrons flow from negative to positive not positive to negative (conventional current) Charge: property of matter - measured in coulombs                                          

EMF = TOTAL VOLTAGE (BATTERY)V = VOLTAGE BETWEEN TWO POINTS

Series: current is the same at all points I = I1 = I2 = I3 = IN V = V1 + V2 + V3… Parallel: voltage is same everywhere V1 = V2 = V3 = VN I = I1 + I2 + I3...

Resistance: measure of how much an electrical component (eg bulb, motor etc.) opposes current flow

Resistance = voltage/currentR = V/Imeasure in ohms

Ohms Law: Voltage is directly proportional to current provided that the temperature remains constant

- bulb/lamp gets hotter- R increases- I increases at a slower rate

Longer wires: more resistanceThicker wires: less resistanceResistance of a wire = directly proportional to its length= inversely proportional to its cross sectional area

Static Electricity

Conductors and Insulators

Current Electricity

Voltage and Circuits

Resistance

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