Physics Section 2: Electricity (COMPLETED)
Physics Section 2: Electricity (COMPLETED)
Ampere (A)- current
Coulomb (C)- charge
Joule (J)- energy
Ohm (Ω)- resistance
Second (s)- time
Volt (V)- potential/energy
Watt (W)- power
In frayed cabling the insulation has worn down exposing live wires, electricity can be conducted from these.
Longer cables are at a higher risk of being damaged and there is more resistance with longer wires making them more at risk of over heating.
Damaged plugs create a risk that some of the safety features may be broken.
Water conducts electricity and can cause energy from the circuit to flow trough it creating a fire and electrocution risk.
Insulation is covering a live wire with a material that won't conduct the electricity.
Double insulation is a precaution that makes sure the live wire cannot touch the casing (so no shock can be conducted) usually by putting extra insulation round that wire. Double insulation can also mean that the casing of an object is plastic so even if the wire touches it, it wont conduct.
An earth wire is touching the case so that if a current is in the case, it will be directed through the earth wire, this will then take the current to the earth. Additionally the surge of electricity in the wire may break the fuse.
Fuses are sections of wire in the circuit that melt if too high a current goes through them. They come with different maximum currents.
Circuit breakers have an electromagnet that is activated if the current goes above a certain limit. the electromagnet pulls an iron switch towards it, this opens the switch and breaks the circuit.
As a resistor slows down the movement of electrons, the kinetic energy that was moving them is converted into heat energy. This can be used, for example, in hair dryers or heaters.
power = current × voltage
P = I × V
energy transferred = current × voltage × time
E = I × V × t
n.b this is the same thing as saying power x time
Alternating current changes from one direction to another rapidly. Mains electricity is alternating
Direct current flows in one direction only. It is supplied by cells and batteries. It comes out as a straight line on an oscilloscope.
energy and potential difference in circuits
In a series circuit everything is connected on one line.
This means that the voltage is shared out between every component:
this makes it useful for supplying low power things like fairy lights.
The current in a series circuit is the same through out all parts of the circuit.
It is worked out using the equation I= V/R.
So its the total of the voltages received by the components divided by the total of all the components resistances.
In a parallel circuit different components are connected separately to the supply.
This means that of one component breaks the others can continue being powered as the whole circuit is still functioning,
It is also good for charging higher power things as the potential difference is equal all over a parallel circuit so each component receives the full voltage.
Current and resistance
If you increase the resistance the current will decrease.
metal filament lamps and diodes all create resistance in a circuit and so will decrease the current.
This can be investigated using an ammeter and measuring the current with and without these components, or with different voltage levels (measured by voltmeter.)
Increasing the resistance will decrease the current. This can be achieved by adding more components or ones with higher resistance.
Decreasing the resistance will increase the current. This can happen if components are removed or replaced by those with lower resistance.
An LDR is a light dependent resistor.
Its resistance changes with the intensity of light: the brighter it is the less resistance; the less light the more resistance.
Thermistors are temperature dependent resistors.
In hot conditions there will be less resistance where as in the cold the resistance is high.
Current is the rate at which charge is flowing through a circuit.
'It is like the flow of water through a set of pipes'
Electric current is a flow of electrons, so when there is an electric current in a metal, the electrons in the metal are flowing.
voltage = current × resistance
V = I × R
Q = I × t
charge = current × time
the energy transferred per unit of charge passed.
The unit volt is a joule per coulomb.
lectrical conductors are materials that allow a current to pass through them.
they need to have 'free' electrons, because current is a flow of electrons.
Metals have free electrons because of the way they are bonded (atoms and electrons within a lattice) this means they are good electrical conductors.
Plastics are polymers which are bonded in a way that means electrons aren't free and so can't move. No flow of electrons means no electric current so they are insulators.
Rub the polyethene rod with a cloth, now the rod will attract the pieces of paper, this is because it now has a charge they are attracted to.
Get a polyethene rod and rip up some small pieces of paper; the rod will have no effect on the paper.
Change in charge
If two materials are rubbed along each other one will gain electrons from the other.
The one that has gained electrons has a negative charge.
he one that has lost electrons will have a positive charge.
The charges are electrostatic because they are not flowing.
Electrostatic phenomena is an event where static electricity has a specific effect:
for example a static shock.
Electrons move from one material to another, the material with a negative charge will then look for some way to earth its charge
like clouds through lightening or a car through your hand and body.
Dangers of Electrostatic
When a large electrostatic charge builds up it can create a spark.
When refuelling vehicles the fuel rubbing along the pipe can cause an electrostatic charge, if this sparks if could ignite the fuel causing a fire or explosion. (This can be avoided if the charge is brought to earth by a wire attached to the pipe or tanker)
Uses of electrostatic
photocopiers and inkjet printers
the ink is given a charge, and the parts of the paper where its wanted is given the opposite charge, so that the ink is automatically attracted to the right parts of the paper.
Charges and attraction
Opposite forces attract.
Similar forces repel.