IGCSE+Electricity+and+Magnetism


 * __4.1 Simple phenomena of magnetism __**

Describe the forces between magnets, and between magnets and magnetic materials Magnetic poles are the parts of a magnet that exert the greatest force. Magnetic poles occur in pairs usually called North (N) pole and South (S) pole. A magnet attracts magnetic materials such as __ i ron __, __ s teel , __ cobalt and __ n ickel. __

Distinguish between magnetic and non-magnetic materials **Magnetic and non-magnetic materials** Magnetic materials can be attracted by the magnet. Iron, cobalt, nickel, steel are magnetic materials. Strongly magnetic metals are called ferromagnetic materials. Non magnetic materials such as cork, glass, plastic, rubber, wood can not be attracted by the magnet.

** Describe methods of magnetisation, to include stroking with a magnet, use of d.c.in a coil and hammering in a magnetic field. ** ** Describe methods of demagnetisation, to include hammering, heating and use of a.c. in a coil **

**Magnetisation** is to give magnetic property by making all the magnetic domains pointing in the same direction.

//Methods of **magnetising** a magnet;// 1. Stroking a steel bar with a permanent magnet 2. Placing a steel bar in a solenoid carrying a large direct current

**Demagnetisation** is the process of removing magnetism from a magnet. __ Heat __ing and __ hammer __ing cause the atoms of the magnet to vibrate vigorously, mixing up the directions of the magnetic domains. The magnetic domains point in random directions. The magnetic effects of the atomic magnets cancel out so there is no resultant magnetic effect.

//Methods of **demagnetising** a magnet;// 1. Heating 2. Hammering 3. Withdraw the magnet that is placed in a solenoid with an alternating current.

1. The more densely packed the field lines, the stronger the field at a point. 2. Magnetic field lines never intersect. 3. The field lines point in the same direction as a compass (from N toward S). 4. Magnetic field lines have no ends they continue through the interior of the magnet. Image from [|cyberphysics] ||
 * Draw the pattern of magnetic field lines around a bar magnet **
 * Describe an experiment to identify the pattern of magnetic field lines, including the direction **
 * [[image:sciencelanguagegallery/magnetic field lines.jpg width="508" height="279"]] || [[image:Magnetic field line by a bar magnet.jpg width="446" height="266"]]
 * The shape of a magnetic field can be shown by __i ron __ __f ilings __ or plotting __c ompasses .__**
 * [[image:Magnetic field lines shown by compasses.jpg width="329" height="288"]][[image:Field lines around a bar magnet.jpg width="359" height="292"]] ||
 * Image from [|BBC bitesize] || Image from PMT wikispaces ||

A magnetic field is a volume of space where magnetic force is exerted.
 * Supplement**
 * • Explain that magnetic forces are due to interactions between magnetic fields **

Images from gcsescience.com || Notice that the lines of magnetic force between the north and south poles are parallel. ||
 * U****nlike poles __ attract __, and l****ike poles __ repel __ each other.**
 * [[image:Like poles repel.jpg width="510" height="323"]]

Give an account of induced magnetism Magnetism can be induced in a magnetic material such as iron if it is placed within a magnetic field. Iron becomes magnetised when they are near or in contact with a permanent magnet.
 * In an experiment with a bar magnet, a piece of wood is held between the N pole of a magnet and two iron nails as shown in the diagram. It is observed that the pointed tips of the iron nails point away from each other.

The iron nails become induced magnets. **The pointed tips of the iron nails are__ like poles (N pole) __ and thus they will __ repel __ each other.** || ||

Distinguish between ferrous and non-ferrous materials

Ferrosmagnetism: The property of being strongly attracted to either pole of a magnet. Magnetic forces tend to push all magnetic moments in the same direction.

A group of atomic magnets pointing in the same direction is called a magnetic domains. Characteristic of substances such as iron, nickel, or cobalt and various alloys that exhibit extremely high magnetic permeability. These are magnetic, **ferrous materials**.

Non ferrous, which is n on-magnetic materials do not attract to magnets. Copper, wood and plastics are **non-ferrous materials**.

Distinguish between the magnetic properties of iron and steel Permanent magnets are made of magnetically HARD materials such as steel. These materials retain their magnetisation once magnetised. SOFT materials, such as iron, lose their magnetisation easily. They are suitable for temporary magnets such as electromagnets.
 * ~ Iron ||~ Steel ||
 * # Easily magnetised
 * 1) Does not retain its magnetism
 * 2) Soft magnetic material
 * 3) Used in electromagnets and in cores of a transformer || # Harder to magnetise
 * 4) Retains its magnetism
 * 5) Hard magnetic material
 * 6) Used to make permanent magnets ||

Distinguish between the design and use of permanent magnets and electromagnets . Uses of permanent magnets
 * ~ Moving coil ammeter ||~ Magnetic door catch ||~ Loud speaker ||
 * [[image:sciencelanguagegallery/moving coil ammeter.jpg width="305" height="239"]]

It consists of a coil suspended in the magnetic field of a permanent magnet. When a current flows into and out of the coil, a turning effect is produced on the coil and the pointer attached to it will move. ||

Magnetic strips are fitted to the doors of freezers and refrigerators to keep the doors closed. || || A magnetic field is also created if an electric current moves through a coil of wire. This is how electromagnets work. (The force between them is at a maximum when the velocity of the charge is perpendicular to the magnetic field.) 1) A moving charge or current creates a magnetic field in the surrounding space. 2) The magnetic field exerts a force on any other moving charge or current present in that field
 * ||  || Magnets are used in moving-coil loudspeakers. At the core of the loudspeaker, there is a very strong permanent magnet. ||
 * Uses of electromagnets**
 * ~ 1. Scrap yard crane ||~ 2. Electric bell ||~ 3. Relay switch ||~ 4. Circuit breaker ||
 * [[image:Scrap yard crane.jpg width="209" height="206"]]

The iron core of the electromagnet is a SOFT magnetic material. When current flows the iron becomes strongly magnetised and so picks up the scrap iron and steel. When the current is turned off the iron loses its magnetisation and so releases the scrap. ||

When the push switch is closed current flows around the circuit turning on the electromagnet. The soft iron armature is pulled towards the electromagnet and the hammer hits the gong. This causes the contact switch to open cutting off the electric current. The spring now pulls the armature back again closing the contact switch. Current now flows again and the hammer hits the gong again. ||

A relay switch is a way of using a low voltage circuit to switch remotely a high voltage (and possibly dangerous) circuit. When switch A is closed, the small current provided by the cell causes the electromagnet to become magnetised.. The iron armature is then attracted to the electromagnet causing the springy contact switch B to close in the high voltage circuit.

A **useful property of relays ** is that the circuit powering the coil is completely separate from the circuit switched on by the relay. For this reason relays are used where a safe low-voltage circuit controls a high-voltage circuit. [|Relays] from BBC Bitesize ||

Current normally flows between terminals A and B through the contact and the electromagnet. When the current in a circuit increases, the strength of the electromagnet will also increase. This will pull the soft iron armature towards the electromagnet. As a result, spring 1 pulls apart the contact and disconnecting the circuit immediately, and stopping current flow. The reset button can be pushed to bring the contact back to its original position to reconnect the circuit || [|Magnet quiz]