Current Electricity It’s all about energy To start off, see if you can arrange these phrases into word equations – You may want to use ‘change of’ in certain places Current Potential Difference (or Voltage) Work Done (or change of Energy) Charge Time Charge

Current Electricity It’s all about energy Current Potential Difference (or Voltage) Work Done (or change of Energy) Time Charge Change of = Charge Change of =

Electrical Energy Electrical Energy is in the form of a higher concentration of electrons in one place rather than another You would have to put work in to squash the electrons together as they all repel each other

Electrical Energy If there is a route for them to even out their concentration they will They will transfer their electrical energy to heat energy

Current Note that charges don’t get ‘used up’ – they just spread out from high concentration to low In a series circuit, the number of charges moving past every point every second is the same Current is constant in a series circuit A1A1 A2A2 A3A3

Inside a Conductor What happens inside a conducting material? The following model of a metal wire could help: At normal temperatures, with no current flowing, electrons hurtle around continuously. They collide with ions but because their movement is random there is no net energy transfer. IonsElectrons

Negative Terminal Positive Terminal Inside a Conductor

Potential Difference (or Voltage) A voltmeter will measure how much more energy there is at one part of the circuit compared to another per coulomb of charge As very little electrical energy is lost as charge travels along conductors V 1  V 2 This is called the Potential Difference V1V1 V2V2

Definitions Charge Property of electrons (and protons) Unit: Coulomb (C) Symbol: Q 1C = The charge carried by 6.25x10 18 electrons Charge on an electron, e = -1.6x C Q = n e, where n is the number of electrons Current Rate of flow of charge. Unit: Ampere (A) Symbol : I 1A = The flow of 1C past a point in 1s. I =  Q /  t Potential Difference Difference in Potential Energy per Coulomb. Unit: Volt (V) Symbol: V 1V = A difference in electrical potential energy of 1 J between two points per coulomb of charge V =  W /  Q

PhET DC Simulation In the class we looked at a simulation showing the movement of charge around a circuit

Questions Have a go at – Page 204 Question 3-5 – Current and Charge Question 9-11– P.D. & Energy

Fun Task! Rearrange the two equations to make  Q the subject in both cases I =  Q /  t V =  W /  Q  Q = I  t =  W / V Now rearrange this to get V I on the left hand side V I =  W /  t Does  W/  t remind you of anything you did in unit 2? V I = Power, P, the rate of change of energy

Negative Terminal Positive Terminal What is resistance? When electrons collide with the lattice they transfer some of their kinetic energy to the lattice

What is Resistance? It is a measure of how good a material is at changing electrical potential energy to another form of energy usually heat The metal ion lattice oscillates because it is warm The oscillations make the electrons more likely to collide with the ions Larger oscillations (higher temperature) mean a larger resistance

Review Pages & give a very good summary of what we have done