A solenoid is a long coil made up of a numbers of turns of wire.

Magnetic Field Pattern

1. Figure (a) illustrates the field pattern produced by a solenoid when current pass through it.
2. The field lines in the solenoid are close to each other, indicates that the magnetic field is stronger inside the solenoid.
3. We can also see that the field lines are parallel inside the solenoid. This shows that the strength of the magnetic filed is about uniform inside the solenoid.
4. We can also see that the magnetic field of a solenoid resembles that of the long bar magnet, and it behaves as if it has a North Pole at one end and a South Pole at the other.

(Figure (a): Magnetic field pattern of a solenoid)

Determining the Pole of the Magnetic Field

1. The pole of the magnetic field of a solenoid can be determined by the Right Hand Grip Rule.
2. Imagine your right-hand gripping the coil of the solenoid such that your fingers point the same way as the current. Your thumb then points in the direction of the field.
3. Since the magnetic field lines always come out from the North Pole, hence the thumb points towards the North Pole.

[Figure (b)]

4. There is another method can be used to determine the poles of the magnetic field forms by a solenoid.
5. Try to visualise that you are viewing the solenoid from the 2 ends as illustrated in figure (c) below.
6. The end will be a North pole if the current is flowing in the aNticlockwise, or a South pole if the current is flowing in the clockwiSe direction.

Strength of the Magnetic Field

1. increasing the current,
2. increasing the number of turns per unit length of the solenoid,
3. using a soft-iron core within the solenoid.

Field Pattern

1. Figure (a) below shows the field pattern produced by a current flowing in a circular coil.
2. In SPM, you need to know the field pattern, the direction of the field and the factors affect the strength of the field.
3. The direction of the field can be determined by the Right Hand Grip Rule. Grip the wire at one side of the coil with your right hand, with thumb pointing along the direction of the current. Your other fingers will be pointing in the direction of the field.

Figure (a)

4. Figure (b) shows the plan view of the field pattern.

Factors Affecting the Strength

There are 3 ways to increase the strength of the magnetic field:

1. increase the current and
2. increase the number of turns of the coil.
3. use coil with smaller radius

Magnetic Field Pattern

(Figure (a))

1. The magnetic field generated by a straight wire are concentric circles around the wire as shown in figure (a) above.
2. Take notes that when the direction of the current is reversed, the direction of the magnetic field line is also reversed.
3. The direction of the magnetic field line can be determined by the Maxwell's Screw Rule or the Right Hand Grip Rule.

(Figure (b): The plan view of the magnetic field generated by a straight wire)

4. Sometime, the magnetic field pattern may be given in plan view, as shown in figure (b).
5. In plan view, a dot in the wire shows the current coming out from the plane whereas a cross in the wire shows the current moving into the plane.

(Figure (c): A dot indicates the current move out from a plane whereas a cross indicates the current move into the plane)

Direction of the Magnetic Field

1. Right Hand Grip Rule or the 
2. Maxwell Screw Rule.

Right Hand Grip Rule

(Figure (d))

(Figure (e))

Strength of the Magnetic Field

1. The strength of the magnetic field form by a current carrying conductor depends on the magnitude of the current.
2. A stronger current will produce a stronger magnetic field around the wire as shown in Figure (f) below.

   (Figure (f))

3. The strength of the field decreases out as you move further out. This is illustrated in figure (g) below. Thus, you must be very careful when you are asked to draw the magnetic field in your exam.

   (Figure (g)

4. The distance of the field lines must increase as it is further out form the wire.

Magnetism

1. a magnet can attract certain type of metal.
2. the metals that can be attracted by a magnet are called the “magnetic materials” of “ferromagnetic materials”. Examples of magnetic materials are iron, steel, nickel and cobalt.
3. a magnet has 2 poles-the North Pole and the South Pole.
4. there is a magnetic field surrounding the magnet.  A magnetic field is a region in the surrounding of a magnet which a magnetic material experiences a detectable force.

Magnetic Field Line

(The magnetic field is represented by the magnetic field lines)

1. The magnetic filed of a magnet is represented by the magnetic field lines. The magnetic field lines flow  out from the North pole and flow into the South pole.
2. The distance between the field lines represent the strength of the field, the closer the field line, the stronger the field. In the diagram, the magnetic field A is stronger than magnetic field B because the line in magnetic field A is closer.

Compass in a Magnetic Field

(Figure(a): The pointer of a compass point towards the North pole of a magnet)

(Figure(b): The direction of the pointer of a magnet is always in the same direction of the magnetic field)

1. The pattern and the direction of a magnetic field can be determined by a compass.
2. First of all, we need to know that, in SPM, normally we use a circle with an arrow to represent compass. The arrow represents the pointer of a compass and it always points towards the North pole of a magnet.
3. Second, we also need to know that the pointer of a compass is always in the direction of the magnetic field.
4. In figure (b) above, we can see that when a few compasses are put near to a bar magnet, the pointer of the compasses are all in the direction of the magnetic field.
5. If a compass is placed near to a current carrying wire, the pointer of the compass will point along the direction of the magnetic field generated by the current (as shown in the figure below). This will be discussed in electromagnetism.

1. When current passes through a conductor, magnetic field will be generated around the conductor and the conductor become a magnet. This phenomenon is called electromagnetism. 
2. Since the magnet is produced by electric current, hence it is called the electromagnet.
3. An electromagnet is a type of magnet in which the magnetic field is produced by a flow of electric current. The magnetic field disappears when the current ceases.
4. The magnetism of an electromagnet is switched on or off using electric current.
5. In short, when current flow through a conductor, magnetic field will be generated. When the current ceases, the magnetic field disappear.