physics Electricity

Current: rate of flow of charge in circut

Potential Difference: AKA voltage difference in potential betwee 2 points in a circut. causes current to flow

Charge: amount of elctricity traveling through a circut

Resistance: anything that slows down the flow of charge around a circut. usually cased by electrons coliding wih ions in material.

Series circut: circut with a single loop of wire

Parallel circut: circut with two or more loops of wire

An electrcal current is the flow of charge, usally electros, around a circut. Size of electric current is rate of flow electrical charge. 

in a series circut the current is the same at any point of the loop.

charge flow (c) = current (A) x time (s)

Q=I t

eg: current of 1.2 A flows through a ire for 5 mins, work out the charge.

5 mins= 300 seconds, Q=I t, Q= 1.2 x 300, Q= 360c

The current through a component depends on both resistance and the potentil difference across

the greater the resistance, the smaller the current for a given PD acrosss the component

Potential Difference (V) = Current ( A) x Resiatnce (Ohms)

V= I R             

e.g, a resistor is placed in the circut as shown 

work out resistance

V= I x R, R= V/I, R= 9.4/ 0.2, R= 47 ohms

• Ohmic Conductors:
• some resistors have a fixed value that doesnt depend on the current flowing through circut. these are ohmic conductors.
• Ohms law states that the current throughout an ohmic conductor is directly proportional to the P.D across resistor. they will produce a straight line grap I -V through the middle (x=y)
• Filament Lamp: The resistance of components usch as lmps, diodes, thermositors, and LDR's is not constant- changes with current through the component.--> non ohmic (lamp or lightbulb).
• as the current icreses the temp of fillament also increases thus the resistance of bulb increases.
• diodes: only allow current flow in one direction. low resistance in foward direction but high resistance in reverse direction
• Thermositors: type of resistor that varies with temperature. resistance decrease as temp increases. used in boilers at home.
• LDR's: light dependent resistors- resistance varieds with light intensisty. resistance decreases as light intensity increases. used as switche to turn on street lamps

•  one loop of wire
• same current through each component
• total potential difference of power supply is shared between the components
• the total resistance of the two components is the sum of the resistance of each component R(total) = R1 + R2 

• consistes of 2 or more loops of wire
• potential difference across each component is the same
• the total current through the whole circut is the sum of the currents through separates components on eachh branch
• the total resistance of the two resistors is less than the resistance of the smallest individual resistor.

a = a1+ a2+ a3

• A direct potential difference will produce a direct current (dc) a current in which the charge carries move in one direction only--> batteries are (dc) DOESN'T GO BELOW 0V

• An alternating potential difference will produce an alternating current (ac) a current in which the charge carries move backwards and fowards--> mains electrcity is ac. GOES BELOW 0V
• In the uk the mains is upplied at aprox 230V, 50Hz 
• does change slightly thus lights get dimmer and brighter at various times.
• lights usally dim when a comercial starts on tv during a big show as lots of people get up to put on the kettle on so demand increases.

• Live= brown-- carries alternatig potential difference from the supply.--> can be dangerous 
• Neutral= blue-- completes the circut
• Earth=yellow/green-- saftey wire to stop appliance becoming live

• the P.D between the live and earth(0v) is 230 V
• neural wire is close to earth potential (0V)
• earth wire only carries a current if there is a falult
• any connection between live and earth can cause current to flow --> electrical fires if too high, eletrocution if a person is making the connection

• power: when electrical appliances are connected into a circut energy is transfererd to the appliance. the rate at which energy is transferred to the appliance is the power rating.

Electrical component--->Power (watts)= potential difference (V- volts) x current (A-amp)   P=V I

Alternative---> Power (w)= (current)^2 x resistance (R-ohms) P= I^2 R

e.g, A microwave is powered by mains electricity at 230v. it has a power rating of 800w-- calculate current

p= i v, i= p/v, i=800/230, i= 3.5A

e.g, a powerline is 100 miles long and carries a current of 400A. resistance of 27.5 ohms calculate power loss in 100 mile length.

P= I^2 R,  P= (400)^2 x 27.5,  P= 4.4MV or 4,400,00 W sooo power loss is 4.4 mv per 100 miles

• everyday electrical appliances are designed to bring about energy transfers.
• amount of energy an appliance transfers depends on how long the appliance is switched on for and the power of the appliance.
• convert energy from ac mains or batteries inro more useful forms
• motors-- electric into kinetic
• lightbulbs--electrical into light
• heaters-- electrical into heat
• some will be transferred usefully some will be wasted (surrounding)

work is done when charge flows in a circut-- amout of energy transferred by electrical work=

energy transferred (j)= power (W) x time (s)--- E= P t

energy transferred (j)= charge flow (C) x P.D(V)--- E= Q V

the nationl grid is a system of cables and transformers linking power stations to consumers 

power stations-> set up transformer-> national grid system-> step down transformers-> consumer

• set up transformers are used to increase the potential difference from the power station to transmission cables.
• step down transormers are used to decrease to a much lower value the potential difference for domestic use in homes

• electric current geerates heat as it moves through electrical wires.
• if transferred at a very high potential differnce and low current means less energy is wated more efficient
• step up- increase the potential difference and decrease the current
• step down- decrease potential differnec and increase the current

a lower potential differnce is used in the home as it is safer so a step down transformer is used near homes and offices