Rate of flow of charge from positive to negative a) Electron b) Ions Charge & current worksheet homework ANSWERS Coulomb (As) Rate of flow of charge from positive to negative a) Electron b) Ions The direction a positive charge would move in a circuit (i.e. Towards the negative electrode) 216C 3.2x10-5A 1.7x103C 1.3x1019s-1

Total out of 14 Charge and current worksheet homework ANSWERS 9) a) 2.0x10-3s = 2ms 9) b) 1.1x1020 10) a) Q=It 10) b) Area under graph is area of rectangle = It 10) c) (1.2x600) + (1.2x50x0.5) = 750C Total out of 14

Estimate the velocity at which an electron travels through a wire (or an ion through an electrolyte)

Mean Drift Velocity 01/08/2018 LO: Attempt to measure drift velocity! Derive drift velocity formula Revise GCSE Chemistry and relate to Physics Become very confident with the concepts involved in the drift velocity formula

Experiment – Use potassium permanganate to attempt to measure the velocity charge carrier move in a circuit. Potassium permanganate crystals placed at the negative end Ammonium Hydroxide + pipette Power pack at 20V 2 needles Ruler Stop clock

The mean drift velocity, v is the average velocity of an electron as it travels through a wire due to a potential difference (p.d). So why do electric devices work instantaneously when a switch is turned on?

Deriving an expression for drift velocity Consider a piece of conductor of cross-sectional area, A and length, l which contains n free electrons per unit volume, each carrying a charge, e. v A l n is known as the number density (number of free electrons per unit volume)

The volume of the wire is: The total number of free electrons N is: N= So total charge of free electrons Q =

If a p.d is applied to either end of the conductor, a current, I will flow: I = Q t Substituting in for Q gives us: I = Notice that l/t is the equivalent of velocity, so: Where v is the mean drift velocity of the electrons

What if I’m asked to work out number density? You will need to work out how many atoms there are per m3 of the conductor. Chemistry  The molar mass tells you the mass of 6.02x1023 (NA) atoms The density tells you the mass of 1m3 of the conductor Density/Molar mass tells you the number of moles in 1m3 of the conductor Multiplying by NA tells you how many atoms per m3

The density of copper is 8900 kgm-3 In copper, there is one free electron for every atom. Determine the drift velocity if a current of 5A flows through a copper wire of cross-sectional area 3x10-6 m2. The density of copper is 8900 kgm-3 The molar mass of copper is 0.064kgmol-1 n = (density / molar mass) x NA n = 8.37 x 1028 I = nAve 5 = 8.37 x 1028 x 3 x 10-6 x 1.6 x 10-19 v v = 1.24 x 10-4 ms-1

What type of materials would have very few or even no free electrons per unit volume? Insulators have very few or no... Semiconductors have intermediate properties (but still ~1million times lower number density than metals). Their number density can be altered by ‘doping’ with different materials e.g. Arsenic

A semiconductor has far fewer free electrons than copper A semiconductor has far fewer free electrons than copper. If a copper wire and semiconductor of equal cross sectional area have a current of 0.5A, which material has the highest drift velocity? Semiconductors – fewer electrons – much few collisions – higher drift velocity

Calculations: AS Electricity Specimen Questions Qu 1-3 pg 87 in textbook Electrons in copper Due

What would you say the key points from today’s lesson were?