Course 7: Electronics

Course 7: Electronics

Electrical Principles Topic 2: Electromagnetism All copyright and intellectual property rights in respect of materials developed by the service provider during this project will vest in the Department of Higher Education and Training, which will have the right to allow any individual, company, agency or organisation to use or modify the materials for any purpose approved by this Department, including selling the materials or releasing them as Open Educational Resources (OER) under an appropriate copyright license. Assumed prior learning 05_01_00 05_01_02

05_02_01 05_03_01 05_04_01 Outcomes By the end of this unit the learner will be able to: 1. Describe what magnetism is 2. Describe the characteristics of magnetic field or flux lines 3. Write an expression for calculating the strength of a magnetic field

Unit 2.1: What is Magnetism? Electricity and Magnetism - Magnetism: Crash Course Physics - Introduction Electricity and magnetism are oppsosite sides of the same coin which is why we use the term

Electromagnetism. To understand how motors, generators, transformers, contactors and relays work, you need to understand magnetism. Magnetism, like electricity is an invisible force. We know its there because we can see its

Electricity Electromagnetism Magnetism What are magnets? Magnets are metals that have the ability to attract or repel other metals. This force is called magnetism. Click on each image to learn more about the basic different kinds of magnets

Img02 Img03 Natural magnets Artificial magnets Natural magnets

Natural magnets have magnetic properties in their natural state. The earth is an example of a natural magnet. Other examples are lodestone (or magnetite), ferrite and pyrrhotite. Magnetism was first discovered because of the magnetic properties of lodestone. Polished lodestone

Artificial magnets Artificial magnets are man-made. They can either be permanent or temporary magnets. Materials that can be magnetised are called ferromagnetic. Img05 Permanent magnets are normally made out of iron or nickel. They keep their magnetism for a long time and can be made using various processes.

Img06 Temporary magnets keep their magnetism temporarily and are normally electromagnets. These can be turned on and off by turning an electric current on and off. Field lines All magnets have a North and a South pole. The magnetic field is

visualised by field lines or flux lines that run From North to South From South to North inside outside the magnet the magnet Img07 Magnetic field lines always form closed loops.

Img08 Opposites attract Looking at their magnetic field lines, we can see how magnets interact. The field is strongest where there are more field lines. Click on the image that shows attraction?

Interacting field lines When magnets interact, their field lines never join or cross. Instead complicated flux patterns are formed. Click on the image that shows repulsion. More on field lines

Here are some more field line drawings. Notice how we always drawn field lines from North to South outside the magnet and how the field lines never join or cross. Click on each image to see a larger version.

Magnetic field strength The strength of the magnetic field is determined by the number of field or flux lines in an area around the magnet. The more field lines the stronger the magnetic field. Click on the image that shows the strongest magnetic field

Img16 Magnetic field strength equation We can express the magnetic field strength mathematically. Click on each symbol to learn what it means. B=

A Lets review We are coming to the end of this unit. Lets review what we have learnt so far. Watch these videos for a brief summary of what we have learnt. YT01

YT02 A Quick Summary Here is a quick summary. Click on the numbers to see each point. 1 Magnetic flux lines travel from N to S. 2 Each magnetic flux line forms a closed loop. 3 Magnetic flux lines never intersect or join. 4

Magnetic flux lines cannot be broken; they just warp into complicated patterns Test Yourself We have come to the end of this unit. Answer the following questions to make sure you understand what magnetism is. Question 1 Which diagram correctly depicts the magnetic field lines. a)

b) Img17 c) d) Img18 Img19

Question 2 Which diagram shows the weakest magnetic field. a) b) Img16 Question 3 Like poles a) Attract

b) Repel Question 4 True or false. Anything can be made into a permanent magnet. a) True b) False Question 5 Which expression gives the magnetic field strength?

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