Electricity and Magnetisum Flashcards
Negatively Charged
Gain electrons, so an excess amount of electrons.
Positively Charged
Lost electrons, so an excess amount of protons.
Conductor
Substance in which electrons can move freely e.g metals
The charge is spread out over the surface evenly because of the electron transfer. More electrons at the corners than a flat surface due to electron movement.
Only conductors can be charged by contact.
Insulator
Substance in which electrons cannot move freely e.g plastics
Only the part that becomes rubbed is charged.
Only insulators can be charged by friction.
Charging by Friction
Objects become electrically charged by being rubbed together, electrons are transferred from one object to another, objects gain equal but opposite charges.
Charging by Contact
Uncharged objects can become charged by coming into contact with other charged objects. They will gain the same type of charge as the charged object.
Earthing
The Earth is a conductor and because of its large size can be considered to be an infinite store of charge, If a charged object is connected to the Earth via a conductor, electrons will flow to, or from, the Earth in order to discharge it.
Electrical discharge to the air
Over time electrons will gradually be lost to (or gained from) the molecules in the air. This happens more quickly if the air is humid.
In a series circuit, the current …
… is the same though out
In a parallel circuit, the current…
… splits up
In a series circuit the voltages around the circuit…
… add up to the supply voltage
In a parallel circuit each branch receives…
… the same voltage
Voltage (V)
Voltage is a measure of how much energy electrons gain or lose around a circuit.
Current (I)
Electrical current is the rate of flow of electrical charge (usually electrons).
Fuses
A fuse is a safety device that prevents currents becoming too high in a circuit. They are a piece of metal wire that heats up as the current increases.
Electrical Power (P)
The power of an electrical device tells us how much electrical energy it converts into other forms of energy each second. Measured in Watts (W)
Magnetism
A magnetic field is a region where magnetic forces can be detected. The field lines:
- show the direction of the force on the North Pole of a magnet if it were to be placed in the field
- are close together where the field is strongest
Magnetic Field Strength (B)
The strength of a magnetic field has the symbol, B, and the units of Tesla (T)
Electromagnetism
When charged objects, such as electrons, move they create a magnetic field around them.
Conventional Current - the original direction current was thought to flow ( + ==> - )
Electron Flow - the actual directions the electrons move (- ==> +)
Solenoids
If a wire is coiled up to form a solenoid the magnetic field around each turn of wire interacts to create a stronger field. The direction of the field will depend on the direction that the current flows. Right hand ruled (thumb points to north)
Electromagnets
If the solenoid is given an iron core then the strength of the magnetics field will be further increased - an electromagnet has been created.
“Soft” iron means that it loses its magnetism when the current is switched off.
“Hard” iron remains magnetised
Paying for Electricity
The joule is a very small amount of energy and so another unit of energy is used by power companies, the kilowatt-hours (kWh).
kWh = kW / h
Cost = (kWh used) x (cost per kWh)
Applications of Electromagnets
Relays
Speakers
