Magnetism

Magnetism Magnetism

Objectives Explain the term ‘magnetic field line.’ Sketch and recognise the magnetic field pattern for a permanent bar magnet, and between two bar magnets. Explain how to use two permanent magnets to produce a uniform magnetic field pattern.

Attraction & Repulsion

Magnetic Materials Steel / Iron Aluminium Ceramics Gold Nickel Plastic Note: Nickel is not the main component of cells, but is present in modern rechargeable cells. Ceramics Gold Nickel Plastic Glass Cobalt Wood Copper Stone

Magnetism S N

Magnetism Which direction is the magnetic field? Where is the magnetic field strongest? S N

Magnetic Field Lines Magnetic field lines show the volume of space around a magnet in which magnetic forces act.

Magnetic Field Lines Field Line Rules: Magnetic field lines of force show: the shape of the magnetic field. the direction of the field lines – north to south. the strength of the magnetic field – closer together = stronger.

Magnetic Field Lines N S

Magnetic Field Lines N N

Magnetic Field Lines

The Earth’s Magnetic Field

Making Magnets Magnetism can be induced in magnetic materials by: Placing them in a magnetic field. Stroking them with another magnet. Magnetic materials can be hard or soft: Magnetically soft materials gain and lose their magnetism easily. Magnetically hard materials are harder to magnetise, but they retain their magnetism.

Magnetism Sequencing Magnets attract or repel other magnets. Magnets can attract magnetic materials such as nickel, iron, steel, and cobalt. A magnetically hard material retains its magnetism after it has been magnetised.

Magnetism Sequencing A magnetically soft material loses its magnetism easily after it has been magnetised. Around every magnet there is a volume of space called a magnetic field.

Magnetism Sequencing Magnetic field lines show three things: the shape of the magnetic field, the direction of the magnetic field, and the strength of the magnetic field. Magnetic field lines that are closest together are where the field is the strongest. A current carrying wire will create a magnetic field around it.

Magnetism Sequencing The strength of the magnetic field around a wire can be increased by increasing the current or wrapping the wire into a coil. The strength of the magnetic field around a solenoid can be increased by increasing the current, increasing the number of turns, or using an iron core.

Loudspeakers Loudspeakers use alternating current. As the current changes direction, so does the magnetic field around the coil. This causes the direction of the force (motion) to change. The continued alternating motion makes the membrane move in and out – making sound waves.