15 May 2014
Static electricity is due to electric charge building up and friction.
A neutral object has an equal amount of protons and electrons and becomes
Negatively charged when it gains electrons.
Only electrons transfer in an atom and are transferred by friction.
+ + = repel
+ - = attract - - = repel
Uses of static electricity
Photocopier - the coping plate is given a charge. An image of the page is projected on the
Charged copying plate. Where light hits the plate and the charge leaks away leaving a pattern on the page. Black ink powder is attracted to the charged parts of the plate. Blank ink powder transferred onto the paper. The paper is heated so the powder melts and sticks to the paper. This is now a photocopy.
Car paint sprayer - the spray gun is positively charged so every paint particle is also. The car given a negative charge so attracts paint. Less paint wasted. Vehicle receives even coat and covers shadow zones.
Smoke precipitator - smoke is solid particles. The smoke particles are given a negative charge when are passed through negatively charged grid. so they are attracted to positive collecting plates. Plates are knocked to remove particles.
Earthing of fuel pipes - an object they may be charged is connected to the earth through an earth wire so charge flows through pipe. This is down with aeroplanes and lorries preventing sparks igniting for a fire or explosion.
AN ELECTRIC CURRENT IS THE FLOW OF NEGATIVELY CHARGED ELECTRONS THROUGH CONDUCTING MATERIALS AND IS MEASURED IN AMPS. ELECTRIC CHARGE IS MEASURED IN COULOMB. AMOUNT OF ELECTRIC CHARGE THAT MOVES IN A CIRCUIT DEPENDS ON THE CURRENT FLOW AND HOW LONG IT FLOWS FOR. CHARGE = CURRENT X TIME
COULOMB AMP SECONDS Q I T
Parallel and series circuits.
Parallel - multiple pathways
Series - one pathway / route.
¥0 or Junction
Series circuit - potential difference is shared. Bulbs are resistors.
Parallel circuit - potential difference same for all bulbs. V=V1=V2
Series circuit - current stays the same throughout
Parallel circuit - the current is split between the two pathways.
Current, potential difference and resistance.
Resistance is the push against the flow of electrons so reduces the size of the current.
Causes of resistance
Resistance = P.D ÷current
RI v." X
Resistance is measured in ohms - Ω A resistor reduces current. A variable resistor allows its resistance to be changed.
A fixed resistor has a resistance that remains the same.
Low current gives a dim light bulb and low resistance in bulb.
High current gives a bright light bulb and a high resistance in bulb.
This is because there is more electron and collisions into the atoms of tungsten causing friction and resistance which gives heat and the bulb has the most resistance when it is hot.
V= energy per unit charge.
Resistance constant current Voltage
Steeper the gradient
Of the line the lower the resistance.
Ohms law :
"the current through a resistor is directly proportional to the Potential difference applied to it as long as the temperature remains constant".
The resistance would be constant at a constant temperature Transferring energy
When current flows through a resistor energy is transferred to the resistor so it warms.
A current in a wire is a flow of electrons, as the electrons move in a metal they collide with the ions in the lattice and transfer energy to them.
Power is the energy transferred every second.
is P = I x V