The Van de Graaff Generator
The dome charges up when the generator is switched on...Sparks are produced if the charge on the dome charges up too much. It charges up because :
-the belt rubs against a felt pad and becomes charged
-the belt carries the charge onto an insulated metal dome
-sparks are produced when the dome can hold no more charge
When an something gains electrons = negatively charged...When something loses electrons = positively charged
Rubbing a polythene rod with a dry cloth transfers electrons to the surface atoms of the rod from the cloth, so the polythene rod becomes negatively charged
Electrical current is the rate of the flow of charge
A metal object can only hold charge if it is isolated from the ground
A metal object is earthed by connecting it to the ground
If a metal object gains too much charge it will produce sparks
If a conducter is supplied with more and more charge, its electrical energy increases. The potential difference (voltage) between the conductor and ground increases, which could cause a spark to jump from the charged object to any nearby earthed object.
Uses of static electricity
Electrostatic paint sprayer: The spray nozzle is connected to the positive end of an electrostatic generator. The negative end is connected to the metal panel. The panel attracts paint droplets from the spray. The droplets of paint all pick up the same charge and repel each other, so they spread out evenly.
Electrostatic precipitator: These are used in coal-fired power stations to remove ash and dust from the gases released into the atmosphere. The particles of ash and dust pass through a grid of wires. The grid wires are negative so the particles become negatively charged when they touch it. The charged particles are attracted onto the positively charged metal plates and the plates are shaken at intervals to remove the ash and ust that builds up on them. *(See next page for diagram)*
Every component has it's own symbol; A circuit diagram shows how components are connected together; A battery consists of two or more cells connected together.
- Components are connected from end to end
- Total resistance is the product of all the resistances added together
- If one component is removed or disconnected the circuit is broken
- Same current in all parts of the circuit
- Total voltage of the supply is shared between components
- The bigger the resistance of a component, the bigger its share of voltage
- Each component separately connected
- All components get the full source voltage (therefore the voltage is the same in all the components)
- The lower the resistance of a component the greater the current
- Total current in the circuit is equal to the sum of the currents in its separate branches
- Total current going into a junction is equal to the total current leaving it
Cables consist of three insulated copper wires surrounded by an outer layer of flexible plastic.
Sockets and plugs are made of stiff plastic which enclose the electrical connections.
In a three pin plug, the live wire is brown, the neutral wire is blue and the earth wire is green and yellow. The earth wire is used to earth the metal case of a mains appliance.
A fuse contains a thin wire that heats up and melts, cutting the current off, if too much current passes through it.
A circuit breaker is an electromagnetic switch that opens and cuts the current off if too much current passes through it.
The power supplied to a device is the energy transferred to it each second.
POWER SUPPLIED = CURRENT xPOTENTIAL DIFFERENCE
(watts) (amps) (volts)
Electrical Energy and Charge
CHARGE = CURRENT x TIME
(coulombs) (amps) (seconds)
ENERGY TRANSFERRED = POTENTIAL DIFFERENCE x CHARGE
(joules) (volts) (coulombs)