Electricity

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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 wire

cell 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/T

current = 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/Charge

V = E/Q

Voltage: Current x Resistance

V = 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/current

R = V/I

measure 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 resistance

Thicker wires: less resistance

Resistance 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