CONDUCTION OF ELECTRICITY . 1.4 (a)Understand how attraction and repulsion between rubbed insulators can be explained in terms of charges on the surfaces of these insulators, and that just two sorts of charge are involved;.
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What happens? What charge does is gain?
A coulombmeter stores the charge it measures
Try using the acetate rod.
Why there is a maximum charge that you can accumulate?Class Experiment 1
What happens to the force of attraction/repulsion as you bring the rod closer?
What is the name of the force acting on the rods?Class Experiment 2
The origin of the word ‘electron’
Complete sheet – ‘Materials that cause static electricity’
Thales of Miletus, William Gilbert
Electron wavefunction visualization
Rutherford gold foil
Proton cancer therapy
Ernest Rutherford is generally credited with the discovery of the proton.
The Englishname electron is a combination of the word electric and the suffix -on, with the latter now used to designate a subatomic particle.
Both electric and electricity are derived from the Latinēlectrum, which in turn came from the Greek word ēlektron (ήλεκτρον) for amber; a gemstone that is formed from the hardened sap of trees (the ancient Greeks noticed that amber, when rubbed with fur, attracted small objects).Electron and proton
Using two metal spheres and a charged polythene rod, charge by induction
Use a nanocoulombmeter to measure the different polarities and magnitudes of charge.Class Experiment 4 - Charging by induction.
Electrons are easily removed or added to an object by vigorously rubbing an object (rod) with another object (fur, silk, etc)
There are two types of charge: positive, which is the absence of electrons and negative which is the excess of electrons
Charge is always conserved
When two objects touch the electrostatic electrons transfer from one object to another until equilibrium is reached
Charge by contact results in both objects having the same type of charge
When a charged object is adjacent (but not touching) to an uncharged object the charges in the uncharged object redistribute
There is no change in the net charge of the uncharged object
An object charged by induction has the opposite charge as the charging object
Initially the charge on the uncharged object polarizes and then a ground is provided to remove some of the charge
The two objects never touch each otherImportant Concepts
Work out how many electrons have moved to produce the charge measured.
Repeat rubbing for 40 and 60 seconds.Class Experiment 5- Calculating the number of electrons.
Fix a metal spoon to an insulating handle, touch it onto the terminal of a high voltage supply, and carry the spoon across to a nanocoulombmeter, onto which the charge is dumped.
Repeat the action
What do you notice?
Try the spoon upside down. Does this make a difference?
Try a bigger spoon. What happens?
Try a bigger potential difference from the supply. What happens
Knowing the charge on an electron, calculate the number of electrons in a 'spoonful' of charge.
internal 50MW resistor
5 kV supply
link to earth socket
bare 4mm plug
metal disk on 4mm plug
coulomb meterDemonstration 1 'Spooning' charge
1.4 (g) understand that electric current is rate of flow of charge;
1.4 (h) recall and use the equation I = ΔQ/Δt;
1.4 (i) recall that current is measured in ampère (A), where A = Cs-1;
Then discharge it by connecting a microammeter to it.
Observe the microammeter as the coulombmeter discharges.Class Experiment 6- Discharging a coulombmeter
The current is measured using a nanoammeter and is controlled using a resistor.
The capacitor is a nanocoulombmeter and so both the current and charge can be measured; the charge should be measured every 5 seconds.
Data should be measured for different currents
Plot a graph of charge against time for the different currentsClass Experiment 7- Charging a coulombmeter with a known current
Current is measured in amperes
1 ampere = 1 coulomb per second ( 1 Cs-1)
Where I = current and ΔQ is the charge that flows in a time Δt.
The coulomb is not a base unit
The base unit for Charge = As
The rate of charge transfer may not be constant. It could be continually changing with time.
If so, the size of the current at any time is the gradient of the graph of charge against time.
Charge can be found by working out the area of a current time graph
Hang a conducting ball in the gap and let it touch one plate.
The ball can deliver charge, the ball shuttles to and fro between the plates.
A sensitive current meter connected between the plates shows that a current is flowing. It is likely to be only a few microamperes.
You can calculate the charge carried by the ball if you know the current and the time of travel of the ball between the plates, because the current is the rate at which the ball carries charge across the gap.
With a constant p.d., move the plates to different distances apart and measure the number of shuttles per second (of the ball) and the current.
Then fix the distance between the electrode plates, vary the p.d. and measure the number of shuttles per second (of the ball) and the current.
On the lap tops, plot graphs of current against number of shuttles per secondDemonstration 6- Shuttle ball
1.4 (k) derive and use the equation I = nAve for free electrons
2. Ions in a current may move very slowly.
What do you think will happen when the electrons enter the more resistive constantan wire?Calculate the drift velocity of electrons in a circuit
n copper = 8.0 x 10 28
n constantan = 3.4 x 10 28