L Theory 1 Flashcards
Electrons
Electrons are held in orbit to the nucleus by a force of attraction. Negatively charged.
Balanced atom
equal amount of protons and electrons
Valence
The outer most orbit of the atoms is the valence shell, the electron here is called the valence electron.
Electron flow
The electrons will flow from the negative plate to the positive plate.
Conventional current flow
This was the belief before that the electrons would flow from positive to negative which is incorrect.
Potential difference
PD will exist between any two points in a circuit having a difference in charge i.e. one side has more electrons than the other.
EMF
Electromotive force
Voltage production: Chemical
negative plate, positive plate. Container, electrolyte and direction of electrons.
Voltage production: friction
By rubbing certain materials together you will allow the electrons to move and transfer between them.
Voltage production: induction
The key thing is the three prerequisites required to cause magnetic induction – A conductor (wire), a magnetic field and movement.
Voltage production: Pressure
Piezo crystals- used in air bag sensors or some lighters
Voltage production: heat
Thermocouple
Voltage production: light
Semi-conductors
Voltage production: light
Semi-conductors
Insulators
Wood Paper Rubber Mica Insulating varnish Porcelain Plastic Woven fabrics Glass
Conductors
Copper Brass Silver Carbon Impure water (salt water) Aluminium Platinum Mercury Gold
Four factors affecting resistance
Type of material, length, cross sectional area and temperature.
Length
Longer the cable the more resistance
Cross sectional area
Bigger the area, the less resistance
Temperature
Increase the temperature you will increase the resistance.
Omhs law
current is directly proportional to the applied voltage, as long as the temperature remains constant. Current is inversely proportional to the resistance
Series circuit formula
RT= R1+R2+R3
Definition of power
The rate of doing work
Definition of electrical power
Number of electrons to be moved and the rate at which they are made to travel
How many watts in 1 horsepower
746
What are fuses used for
Protecting the supply
What are the two types of fuse used in the RN
Cartridge and rupturing capacity fuse
How does a fuse work
Once a fuse blows it breaks the circuit which means no more current can flow as there is no potential difference. If the gap between the two ends of the fuse is small then sparking can occur so to stop this, quarts powder fills the gap.
What is the voltage of earth
0 volts
The two types of earth return circuits
series and parallel
What material does magnetism derive from
Magnetite
What direction does a magnetic field travel
North to south
What are the lines called in a magnetic field
lines of magnetic flux
What happens if you connect two same poles together
They will repulse eachother
What happens if you connect two opposite poles
They will attract eachother
What are the two types of magnets
Horseshoe and bar
Temporary magnets
Materials that become magnetised then lose their magnetism
Materials that produce good magnets
Aluminium, nickel and cobalt
Magnetic induction
a means of creating a magnetic field into a material that is near another magnet
What are the two types of current
AC(alternating current) DC(direct current)
Advantages of AC
With AC you can easily change the voltage size using transformers, therefore, it is more adaptable and the equipment is smaller and lighter.
Measurement of frequency
cycles per second = Hertz
Self inductance
Because we have now created a moving magnetic field, a voltage is self-induced in the coil which opposes the changing AC current input.
What is the unit of inductance
The Henry
Transformers only work with what current
AC
What is the voltage called in a transformers secondary coil
The EMF of mutual induction
What are the two types of transformer
Core and shell
What is put into a transformer to maximise transfer between primary and secondary coils
A soft iron core which enhances the magnetic field
Centre tapped transformer
Connected to sockets supplying portable equipment to reduce the shock hazard by a half
Key components of a single loop generator
Wire loop/armature, poles (north and south), slip rings, carbon brushes and the load.
What is the most common AC generator
Brushless generator
Components from a brushless generator
HF Generator
AVR (automatic voltage regulator)
Rotating rectifier assembly
What does the rotating rectifier assembly do
Takes AC from the exciter rotor and converts it to DC
