# 6 Magnetism and electromagnetism

## 6.03 describe the properties of magnetically hard and soft materials

Permanent magnets are made of magnetically hard materials such as steel. These materials retain their magnetism once magnetised.

Some materials like iron are magnetically soft. They lose their magnetism once they are no longer exposed to a magnetic field. They are used as temporary magnets such as electromagnets.

2019-06-28T10:55:29+00:00Categories: (b) Magnetism, Edexcel iGCSE Physics, Uncategorized||

## 6.04 understand the term magnetic field line

Around every magnet there is a region of space where we can detect magnetism (where magnetic materials will be affected).

This is called the magnetic field and in a diagram we represent this with magnetic field lines.

The magnetic field lines should always point from north to south.

## 6.05 know that magnetism is induced in some materials when they are placed in a magnetic field

 When magnetic materials are bought near or touch the pole of a strong or permanent magnet, they become magnets. This magnetic character is induced in the objects and it is removed when the permanent magnet is removed. This is a temporary magnet Magnetism is induced in the paperclips so each paperclip can attract another one

## 6.06 practical: investigate the magnetic field pattern for a permanent bar magnet and between two bar magnets

1. Place your bar magnet in the centre of the next page and draw around it.
2. Place a compass at one pole of the bar magnet.
3. Draw a ‘dot’ to show there the compass is pointing,
4. Move the compass so the opposite end of the needle is pointing to the dot,
5. Repeat steps 3 and 4 until to reach the other pole of the magnet.
6. Do this procedure at least 5 times from different points on the pole of the magnet.
*Tip, try to be as accurate as possible when drawing your dots*
7. Join up your dots to create the field line plots

## 6.11 know that there is a force on a charged particle when it moves in a magnetic field as long as its motion is not parallel to the field

 The movement of the charged particle is a current so it produces a magnetic field. This magnetic field interacts with the permanent magnetic field to create a force. The force is perpendicular to the direction of motion and the permanent magnetic field.

## 6.12 understand why a force is exerted on a current-carrying wire in a magnetic field, and how this effect is applied in simple d.c. electric motors and loudspeakers

Motor

• Current flows in the wire/coil.
• This creates a magnetic field around the wire/coil.
• This magnetic field interacts with the field from the permanent magnet.
• This produces a force on the wire/coil which moves the wire/coil.
• The split-ring commutator changes the direction of the current every half turn as it spins. This reverses the direction of the forces, allowing the coil to continue spinning.

Loudspeaker

• An alternating current from the source passes though the coils in the speaker.
• This current is constantly changing direction and magnitude
• This current creates a magnetic field around the coil
• This field interacts with the magnetic field from the permanent magnets
• Creating a constantly changing force on the coil.
• This causes the coil to vibrate in and out as the direction of the force changes, moving the cone
• The cone causes vibrations which we hear as sound waves.

## 6.14 describe how the force on a current-carrying conductor in a magnetic field changes with the magnitude and direction of the field and current

 If you increase the magnitude of the current through a wire or the size of the magnet being used, you increase the force on the wire. If you change the direction of the current or reverse the poles of the magnet, you change the direction of the force on the wire

## 6.15 know that a voltage is induced in a conductor or a coil when it moves through a magnetic field or when a magnetic field changes through it and describe the factors that affect the size of the induced voltage

When a conductor (can be a wire, coil or just a piece of metal) experiences a changing magnetic field a potential difference or voltage is induced in it. The strength of the potential difference depends on the strength of the magnetic field, how fast it changes i.e. how fast the coil is spinning, and how much of the conductor is exposed to the field i.e. how many turns in the coil.

## 6.16 describe the generation of electricity by the rotation of a magnet within a coil of wire and of a coil of wire within a magnetic field, and describe the factors that affect the size of the induced voltage

 Electricity can be generated by either moving a magnet inside a coil of wire or rotating a coil inside a permanent magnetic field.   Model answer for a generator (Rotating coil): ·         Coil is rotated within a magnetic field ·         As it turns the coil cuts the magnetic field lines. ·         This induces a voltage (or current) in the coil. ·         This can then be connected to an existing circuit. ·         In a generator, energy is being converted from kinetic (mechanical) energy into electrical energy. ·         The size of the induced voltage (or current) can be increased by: ·         Using a stronger magnet ·         Having more turns in the coil ·         Spinning/moving the coil faster.   Model answer for a generator (Rotating magnet) ·         Magnet is rotated within a coil ·         As it turns the coil cuts the constantly changing magnetic field lines from the magnet. ·         This induces a voltage (or current) in the coil. ·         This can then be connected to an existing circuit. ·         In a generator, energy is being converted from kinetic (mechanical) energy into electrical energy. ·         The size of the induced voltage (or current) can be increased by: ·         Using a stronger magnet ·         Having more turns in the coil ·         Spinning/moving the magnet faster.

## 6.17 describe the structure of a transformer, and understand that a transformer changes the size of an alternating voltage by having different numbers of turns on the input and output sides

 AC current in the primary coil produces a changing magnetic field around the primary coil. The iron core channels the changing field through the secondary coil. The changing magnetic field induces a voltage in the secondary coil.
Select a set of flashcards to study:

Terminology

Skills and equipment

Remove Flashcards

Section 1: Principles of chemistry

a) States of matter

b) Atoms

c) Atomic structure

d) Relative formula masses and molar volumes of gases

e) Chemical formulae and chemical equations

f) Ionic compounds

g) Covalent substances

h) Metallic crystals

i) Electrolysis

Section 2: Chemistry of the elements

a) The Periodic Table

b) Group 1 elements: lithium, sodium and potassium

c) Group 7 elements: chlorine, bromine and iodine

d) Oxygen and oxides

e) Hydrogen and water

f) Reactivity series

g) Tests for ions and gases

Section 3: Organic chemistry

a) Introduction

b) Alkanes

c) Alkenes

d) Ethanol

Section 4: Physical chemistry

a) Acids, alkalis and salts

b) Energetics

c) Rates of reaction

d) Equilibria

Section 5: Chemistry in industry

a) Extraction and uses of metals

b) Crude oil

c) Synthetic polymers

d) The industrial manufacture of chemicals

Go to Top