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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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;
Charge the polythene rod with the duster and rub it onto the nanocoulombmeter.
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
Use a free swinging charged rod and place in turn, a charged acetate and polythene rod next to it and observe attraction and repulsion.
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
1.4 (b) understand that the name negative charge was arbitrarily given to the sort of charge on an amber rod rubbed with fur, and positive to that on a glass rod rubbed with silk;
The origin of the word ‘electron’
Complete sheet – ‘Materials that cause static electricity’
Rub a glass rod with silk and an amber rod with fur, use the nanocoulombmeter to detect any charge.Class Experiment 3
Thales of Miletus, William Gilbert
1.4 (c) recall that electrons can be shown to have a negative charge, and protons, a positive;
Electron wavefunction visualization
Rutherford gold foil
Proton cancer therapy
The negative charge, and protons, a positive; proton (Greekπρῶτον / proton "first") is a subatomic particle with an electric charge of one positive fundamental unit
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
1.4 (d) explain frictional charging in terms of electrons removed from, or added to, surface atoms;
Using a gold foil electroscope, charge it by induction removed from, or added to, surface atoms;
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
1.4 (e) recall that the unit of charge is the coulomb (C), and that an electron's charge, e, is a very small fraction of a coulomb;
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.
Electric charge can be picked up and carried by a spoon, just as if it were sugar or milk!
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 (f) recall that charge can flow through certain materials, called conductors;
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;
Demonstration 2: A filament lamp materials, called conductors;
Demonstration 3: A spark in air
Demonstration 4: Fluorescent tube
Demonstration 5: Electrolysing copper sulphate solutionIdentifying charge carriers
Charge a coulombmeter with a polythene rod to at least -1000nC. (Try by induction)
Then discharge it by connecting a microammeter to it.
Observe the microammeter as the coulombmeter discharges.Class Experiment 6- Discharging a coulombmeter
Charging a capacitor. In order to collect data to show the link between charge and current, it is possible to charge a capacitor up using a cell.
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
The current is the rate of charge or the quantity of charge that flows per second.
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 (j) understand and describe the mechanism of conduction in metals as the drift of free electrons;
1.4 (k) derive and use the equation I = nAve for free electrons
1. Electric currents are made of moving charged particles. in metals as the drift of free electrons;
2. Ions in a current may move very slowly.
Using a micrometer and an ammeter. Take the measurement needed to calculate the drift speed of the electrons through the copper wire and constantan wire.
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