Opposite (unlike) poles attract, and like poles repel. If permanent magnets are repeatedly knocked, the strength of their magnetic field is reduced. Converting a magnet to a non-magnet is called demagnetisation. Magnets are made from magnetic metals - iron, nickel and cobalt.

When a piece of unmagnetised magnetic material touches or is brought near to the pole of a permanent magnet, it becomes a magnet itself. The magnetism is induced. A North Pole induces a North Pole in the far end.

It would be difficult to draw the results from the sort of experiment seen in the photograph so we draw simple magnetic field lines instead.

A bar magnet with several curved lines pointing from the north to South Pole

In the diagram, note that:

- the field lines have arrows on them

- the field lines come out of N and go into S

- the field lines are more concentrated at the poles

The magnetic field is strongest at the poles, where the field lines are most concentrated.

Two bar magnets:

Magnetic field lines for fields involving two magnets.

Note the different patterns seen when two like poles are used and two opposing poles are used.

Iron gets magnetised faster but loses its magnetism as soon as the inducing magnet is removed. Hence soft iron is said to have high susceptibility but low retentivity. Core in the transformer is made up of soft iron material. Steel is slow to be magnetised but retains the acquired magnetism for a long time.

Electromagnets are objects that become magnetic when electricity is flown through it. They are temporary, as their magnetism can be turned on and off by switching an electrical circuit on and off.

Permanent magnets magnetism cannot be turned on and off, they are permanently magnetised.

Procedure:

The steel bar is stroked with the same pole of the permanent magnet from one end to the other end in one direction.

The stroking magnet has to be lifted sufficiently high above the steel bar between successive strokes.

The steel bar will become a magnet with pole produced at the end where the strokes finish is opposite to the stroking pole used as the atomic magnets in the domain are attracted to the stroking pole.

Note:

When using two magnets, the stroking pole used in each magnet has to be opposite, and they stroke the steel bar in opposite direction.

Using two magnets to stoke is faster than that using one magnet.

Stroking method only produces weak magnets.

Procedure:

Connect the solenoid to a direct current (d.c) supply.

Place the steel bar inside the solenoid.

Switch on the d.c supply.

When current flows through the solenoid, a strong magnetic field is produced which magnetise the steel bar.

The pole of the magnetized steel bar is determined by Right Hand Grip Rule.

Note:

Solenoid is made up of several hundred turns of copper wire.

Electrical method is the most effective method of magnetization. It is much quicker than stroking method and produces strong magnets.

Since all materials on earth are made up of atoms which contain the positively charges protons and negatively charged electrons, any imbalance in the number of protons and electrons will cause the material to be charged or ionised. A loss of electrons will make it positively charged and a gain of electrons will make it negatively charged. When you rub the balloon, for example on the carpet, electrons (with a negative charge) build up on the surface of the balloon (they are transferred from the carpet to the balloon). This is called static electricity which means 'non-moving electricity'.

Just like magnetic poles, electric charges also attract when they're unlike and repel when they're like.

The electrons in the ballon, have the power to pull very light objects (with a positive charge) toward them - like the positive ions in the water.

Electrostatic attraction can be produced and observed in simple experiments:

- Inflate a balloon and rub it quickly on any dry surface e.g. a carpet. Then open a tap and hold the balloon next to it (without touching the water). You should see that the water bends towards the balloon.

- Tear up a piece of paper into small bits, then take a ruler, rub it on your hair and place them just above the bits of paper, without touching them. You should see the paper get attracted to the ruler.

- This kind of attraction is called electrostatic attraction. This happens because of the charges on the materials.

Charging a body involves the addition or removal of electrons.

As a region in which an electric charge experiences a force

Conductors are materials in which current can flow. Examples are copper, aluminium, gold and silver.

Insulators cannot conduct electricity. Examples are glass, wood, paper, air and rubber

- Is the flow of electric charge within a circuit

- Is measured in amperes or amps

- Represents how much electric charge is passing a single point in the circuit.

- Is the same at the beginning and end of a circuit.

- Is measured in volts

- Is the difference in the energy there is to drive a current through a wire, between two points

- Electromotive force is the voltage that a battery will supply to the entire circuit.

- Is the driving force that gives the electrons the energy to move around the circuit.

- Is a measure of how difficult it is to push a current through a circuit.

- Is measured in Ohms.

Current is the flow of charge (electrons) within a circuit.

Current is the rate of flow of charge in a given point of the circuit

I = Q/T

I = current, Q = charge and T = time.

Metallic bonding is the strong attraction between closely packed positive metal ions and a 'sea' of delocalised electrons. These delocalised electrons can carry charge and move freely through giant the metal structure, thus making metals conductive of electricity.

Potential represents how much energy there is to drive a current through the wire and is measured in volts.

Ammeter is a device that measures the amount of current flowing through a circuit in amps.

Voltmeter is a device that measures the potential difference between two points in a circuit

Of an electrical source of energy is measured in volts.

Defined in terms of energy supplied by a source in driving charge around a complete circuit

The electrical resistance is a measure of the difficulty to pass an electric current through a conductor.

Resistance is calculated by dividing the voltage between two points by the current flowing through the points.

R = V/I

From this formula, we can conclude that an increase in voltage will increase resistance. Reducing voltage will reduce the resistance.

The graph curves because as the filament has it's resistance goes up (the resistance of the filament is changing)

Current is directly proportional to potential difference. Doubling the potential difference doubles the current in the circuit. The resistance remains the same. Plotting a graph of potential difference against current give a straight line passing through the origin.

If the voltage is 6 volts and the current is 2 amps, the resistance = 6 + 2 = 3ohms.

This formula is known as ohm's law and rearranged to find each of the values.

I = V/R

V= I x R

Resistance is directly proportional to length, denoted as R a length. Resistance is also inversely proportional to cross-sectional area, denoted as

R o

Combining these two we get

R o

We can add a constant p (pronounced as rho, in greek alphabet) to rewrite it as

R = p x (l/a)

In order to find the constant (by what proportion resistance changes with respect to length and cross-section area), we can rearrange the formula to:

p = R x (a/l)