3.4 Generation Of Electricity Flashcards
Production of electricity by light.
When light falls on certain semi conductors it may cause charge separation and therefore generate electricity.
Holes behave as positive charges and extra electrons as the negative charges. Electrons shuffle from one covalent bond to the next to fill the hole, the hole effectively moves the opposite way.
The conductivity of a semiconductor depends on the rate at which crystal bonds are Brocken. The breaking of bonds releases an electron and a hole.
Energy input from light increases vibrations of atoms therefor increasing conductivity.
By adding impurities ( doping ) we can create semiconductors that tend to produce more electrons ( n-type) or more holes (p-type).
A voltaic cell is made by placing a thin slice of of N-type silicon over a thicker slice of p-type.
When light falls on the space where they meet called the p-n junction, an emf is generated.
Strips of metal on the top and bottom act as terminals
Generation of electricity by heat?
Thermal energy directly transferred into electrical energy by thermoelectric effect.
Used in a thermocouple.
Two different types of metals physically joined together which creates a small EMF.
The EMF increases when temperature is increased in a very predictable way
Generation of electricity by friction
Rubbing an insulator causes electrical charges to separate and is a source of EMF.
The electric field is strongest at points and corners.
Static dischargers are used on aircraft to dispel static charges.
Generation of electricity by pressure
Using pressure to deform a piezo crystal generates a voltage, piezoelectric effect.
The pressure seperates charges within the crystal and is therefore a source of EMF.
The action is reversible.
Charges are collected using certain materials as terminals.
Used in crystal microphones, record players, gas lighters.
Generation of electricity by chemical action
Immersing two different pieces of metal into an electrically conducting liquid (eg water and sulphuric acid) generates a voltage between the two electrodes.
Referred to as galvanic cells
Generation of electricity by magnetism and motion.
Moving a conductor at right angles to a magnetic field produced an EMF in the conductor.
As it causes a force to act on the electrons.
Energy is transferred form kinetic energy store in the moving conductor, to electrical energy in the circuit.
