1. ELECTROMAGNETISM

2. FORCE ON A CURRENT CARRYING CONDUCTOR
The current carrying wire has magnetic field around it. If we place the current carrying wire into the magnetic field, the two magnetic fields may interact, and produce a force on the wire. This can be shown by the experiment set up below.

4. When a current is passed through the wire, the wire moves upward
When a current is passed through the wire, the wire moves upward. A force is acting on the wire segment inside the magnetic field.
When the direction of current reversed, the wire move downward.
When there is changing of direction of the magnetic field, the force acting on a wire also change.
When the current and magnetic field strength are increase, the wire experience a large force. The force acting on the wire is therefore proportional to current and magnetic field strength
The direction of force can be determine by Fleming’s Left Hand Rule.

5. Fleming’s left hand rule
Place the forefinger, second finger and thumb of the left hand mutually at right angles. Then , if the forefinger points in the direction of the field and second finger in the direction of current, the thumb will point in the direction of the force or motion.

6. FORCE ON A BEAM OF CHARGE PARTICLE
When a beam of moving charged particles enters a magnetic field, there is a force acting on the charged particles. They are deflected inside the magnetic field. Fleming’s Left Hand Rule can be applied to determine the direction of deflection of the beam of charged particles.
A beam of positive charged particles
Direction of current is same as direction of movement of the charged particles
If beam of positive charged particles enters magnetic field into the paper, the charged particles move towards top of the paper as shown below.

7. When the direction of magnetic field changes the force acting on a charge particle also changes.
If the positive charge particle enters magnetic field out of the page the charge particles move towards bottom of the page. So by using Fleming’s Left Hand rule we can find the direction of force acts on a charged particle.

8. A beam of negative charge particles (electrons)
Current is in an opposite direction to that of the flow of negative charges. If beam of negative charged particles enters magnetic field into the paper, the charged particles move towards bottom of the paper as shown below.

9. When the direction of magnetic field changes the force acting on a charge particle also changes.
If the negative charge particle enters magnetic field out of the page the charge particles move towards top of the page. So by using Fleming’s Left Hand rule we can find the direction of force acts on a charged particle.

10. MAGNETIC FIELDS BETWEEN PARRALEL CURRENT CARRYING CONDUCTORS
When two parallel wires carrying current at same direction, both the wires move towards each other and magnetic field pattern is shown below.

11. When two parallel wires carrying current in an opposite direction, both the wires move away from each other and magnetic field pattern is shown below.

12. D.C MOTOR
A simple direct current electric motor consists of a coil (ABCD) connected to two split-ring commutators (X and Y), two permanent magnets and two carbon brushes (P and Q) connected to an external battery. The commutators rotate with the coil. Two carbon brushes are made to press lightly against the commutators so that current can pass through when they are in contact.

13. (a) When current flows from A to D through the coil, the side CD experiences an upward force and the side AB experiences a downward force. These forces produce a turning effect and cause the coil to rotate in a clockwise direction.

14. (b)When the coil rotates 90° and reaches the vertical position, the contact between the carbon brushes (P and Q) and the commutators (X and Y) are broken. No current flows through the coil. Because of its inertia, the coil keeps rotating until the commutators are in contact with the carbon brushes again.

15. (c) The current along the sides AB and CD is reversed
(c) The current along the sides AB and CD is reversed. The side AB experiences an upward force and the side CD experiences a downward force. These two forces produce a clockwise moment. Hence the coil continues to rotate in a clockwise direction.

16.  The purpose of the split-ring commutators is to reverse the direction of current in the coil whenever the commutators change contact from one carbon brush to another. This ensures that the coil will rotate in a fixed direction. Four ways to increase the rotating speed of a motor: (i) increasing the current, (ii) increasing the number of turns of the coil, (iii) increasing the strength of the magnetic field, (iv) increasing the area of the coil

17. ELECTROMAGNETIC INDUCTION
Electromagnetic induction is the production of an e.m.f (voltage) in a conductor when there is a change in magnetic flux linked with the conductor. When a wire is moved across a magnetic field, as shown below, a small e.m.f. (voltage) is generated in the wire. If the wire forms part of a complete circuit, the e.m.f. makes a current flow. This can be detect by using a sensitive meter called galvanometer.

18. When the direction of movement of wire changes the direction of induced current also changes.
If the wire moves downward, the direction of current carried is shown below and the deflection of galvanometer need is also same direction that is right side.
If the wire moves upward, the direction of current carried is shown below and the deflection of galvanometer need is also same direction.

19. The direction of induced current in the straight wire can be determined by using Flemings Right Hand Rule.
If the magnetic field direction changes the current direction also changes.
If the wire is in rest in the magnetic field, no e.m.f is induced.

20. The factors effecting magnitude of induced e.m.f
The induced e.m.f. (and current) can be increased by:
moving the wire faster
using a stronger magnet
increasing the length of wire in magnet in the magnetic field – for example, by looping the wire through the field several times as shown below.

21. LENZ’S LAW
The direction of induced current can be determined by Lenz’s law.
An induced current always flows in a direction such away that its magnetic field opposes the change which produce it.
Example 1
The N-pole of magnet is moving towards the solenoid as shown in the diagram below.
The change that induces current is the N-pole moving towards the solenoid. According to Lenz’s Law, the direction of induced current opposes the change producing it. To oppose the N-pole moving to the coil, the induced current must produced a N-pole at the end X. Hence the direction of induced current is as shown.

22. Example 2
The N-pole of magnet is moving away from the solenoid as shown in the diagram below.
The change that induces current is the N-pole moving out the solenoid. According to Lenz’s Law, the direction of induced current opposes the change producing it. To oppose the N-pole moving out of the coil, the induced current must produced a
S-pole at the end X. Hence the direction of induced current is as shown above.

23. A.C. GENERATOR
A simple a.c. generator consists of a coil rotating about an axis
between the poles of a permanent magnet as shown below.
When the coil rotates, it cuts magnetic field lines, so an e.m.f. is induced. This makes a current flow through the coil.
As the coil rotates, each side travels, upwards, down wards, upwards and downwards… and so on, trough the magnetic field. So the current flows backwards, forwards and an a.c. current is produced.

24. The induced current can be increased;
The direction of induced current changes every half rotation of the coil and this can be determined by using Fleming’s Right Hand Rule.
The end of coil are connected to a pair of slip rings. The slip rigs rotate with the coil and are in close contact with two carbon brushes which rub against the slip rings and keep the coil connected to the out side part of the circuit.
The induced current is maximum when the plane of the coil is parallel to the magnetic field. There is no induced current when the plane of the coil is perpendicular to the magnetic field.
The induced current can be increased;
using the coil with more turns
using stronger magnet
rotating the coil faster

25. Graph of voltage output against time for a simple a.c. generator

26. TRANSFORMER Transformer is a device used to increase or decrease the
voltage of a.c. supply.
The transformers only worked with alternative current (a.c.).
The diagram below shows how transformer works.
It make use of electromagnetic induction.
When the primary coil has alternative current flowing through it. It is thus an electromagnet, and produces an alternating magnetic field.

27. The core transports this alternating field around the secondary coil.
Now secondary coil is a conductor in a changing magnetic field. A current is induced in the coil.
There are two types of transformers:
1. Step-up transformer
A step-up transformer is used to increase the out put voltage,
so there are more turns on the secondary coil than primary coil
as shown below.

28. 2. Step-down transformer A step-down transformer is used to decrease the out put voltage, so there are more turns on the primary coil than secondary coil as shown below.
The ratio of number of turns tells us the factors by which the voltage will be changed. Hence we can write an equation, known as transformer equation, relating two voltages Vp and Vs, to the number of turns on each coil, Np and Ns.

29. Advantages of high voltage transmission
From the power houses the electricity is transmitting by high voltage, using step up transformer as shown below. This is because using higher voltage for power transmission reduces power loss in the transmission cables.

30. Environmental and cost implications of underground power transmission compared to overhead lines.
To prevent sparking, the only effective way of insulating the cable is to keep huge air spaces around them. That’s why we have to be suspended from pylons. Underground cables are more difficult insulate and must be used at lower voltages, to transmit same power they have to carry higher current. This means that we have to use thicker cables and it will be very expensive to lay. Despite the extra cost.
Underground cables are used in areas of outstanding natural beauty so the destruction of ground.