electricity

current

rate of the flow of charge

charge equation

Q=IT

how much charge passes in 1 second with an ampere of 1

1 coulomb

voltage equation with energy and charge

V = E/Q

when is the PD across a component 1V

when you do 1 joule of work moving 1 coulomb of charge through the component

Drift velocity

average velocity attained by charged particles in a material due to an electric field

equation to calculate current of a wire made out of a certain material

n in the equation for current

number of charge carriers(electrons) per m² of the material

m^-3

q in the equation

amount of charge on each charge carrier

coulombs

V in the equation

drift velocity

ms^-1

A in the equation

cross sectional area

m²

what happens if you double the area of the wire

the current doubles because doubling the area, doubles the amount of paths the charge carriers can flow through making the flow faster therefore

current is directly proportional to area

what happens if you double any one of the values in the equation

the current doubles

what does the resistance of a wire depend on

1. length of wire

   R directly proportional to L

2. area of wire

   R inversely proportional to A

3. type of material(resistivity of material)

   a higher resistivity means it has a lower no of charge carriers

resistivity

a property that describes the extent to which a material opposes the flow of electric current through it

equation for resistivity

why does increasing temp, increase resisitivity

higher the temp of a material, more collisions with atoms due to kinetic energy which increases resistivity

what would a resistance over length graph look like

directly proportional

how to calculate resistivity using a resistance over length graph

gradient = R/L

resistivity = gradient x area

resolution

the smallest change in measurement that a insturment can detect

how to work out absolute uncertainty

AU = plus or minus resolution/2

how to work out percentage uncertainty

(AU/measured quantity) x 100

how to reduce percentage uncertainty

measure large quantities or use an instrument with a highr resolution(lower AU)

EMF

energy per charge supplied by the source

V

terminal voltage - energy per charge used in load resistance

v

lost volts - energy per charge wasted in internal resistance

equation for EMF

V + v

or

I(R + r)

internal resistance

the resistance of the power source which causes lost volts

how to measure EMF

voltmeter around the source - extremely high resistance therfore doesnt allow to current to flow so internal resistance doesnt kick in

practical to find EMF and internal resistance

1. use a voltmeter around source to find EMF

2. use a voltmeter to find terminal voltage

3. use ammeter to find current through the circuit

4. use equation to find internal resistance or plot a terminal voltage against current graph where the gradient is the internal resistance

how to find EMF from a terminal voltage over current graph

the y-intercept because current equals 0 therefore no internal resistance

why does current stay the same through the whole circuit

if current is affected in one part of the circuit its affected throughout the whole circuit i.e more resistance means more voltage - I = V/R

kirchhoff’s first law

conservation of current:

total current entering a junction = total current leaving it

kirchhoff’s second law

when no internal resistance:

the total EMF around a series circuit = the sum of the P.Ds across each component

conservation of energy

resistance in parallel circuits

resistance in series

potential dividers

a simple circuit that divides a voltage into smaller, proportional voltages using resistors

which one of these circuits is more suitable to obtain data?

• both circuits are suitable because they allow readings of current and voltage

• the min PD for the one on the right is 0V

• the min PD for the one of the left is greater than 0V

• the max PD for the one on the right is the supply PD

• for the one on the left adjusting the resistor changes the circuit resistance - sharing voltage

• the one on the left minimum PD depends on the variable resistor

• the one on the right is better because it allows for a bigger range

what value would V be

the difference between the voltages of the resistors