Combined Science (1-9): Electromagnetism Electromagnetic Induction

Objectives:

Electromagnetic Induction Draw a line under last lesson’s work and write today’s title in your book... Electromagnetic Induction 30/11/2018 c/w

FLASHBACK FLASHBACK: Explain the differences between nuclear fusion and nuclear fission

FLASHBACK- AFL

Explain how the speed of a motor can be increased Starter Activity Explain how the speed of a motor can be increased

Explore: Electromagnetic Induction Previously we discussed that when a wire carrying a current is placed within a magnetic field, it will feel a force (motor). Well similarly, when you move/rotate a wire in a magnetic field it will induce a current! This happens when you move a magnet in a coil of wire We do this for small scale emf induction. This is because it’s easy to do in a laboratory! Or when you move a coil in a magnetic field We do this for large scale emf induction. This is because it’s easier to make large coils move than to move large magnets!

Explore: Electromagnetic Induction Voltage (and so current) is induced as the wire cuts through magnetic field this is known as flux linkage Task: Suggest how we could INCREASE the amount of induced current? The current we produce can be increased by: Moving the magnet through the coil quicker Using more coils Using a stronger magnet Task: Referring to linkage explain why these changes will produce a higher current

Try answering this question Explore: Wording in an exam Be careful when explaining how an emf is induced by electromagnetic induction. You need to avoid using the word ‘production’ as the word ‘induced or induction’ could be worth a mark! Try answering this question A student is attempting to use a magnet on a spring to create a current through a coil of wire. He attaches a voltmeter to the coil Task: The student pulls the magnet and then lets it oscillate (bounce) through the coil. Describe the results he will observe and explain what causes it.

Explore: Practice Question Task: The student pulls the magnet and then lets it oscillate (bounce) through the coil. Describe the results he will observe and explain what causes it. First, describe the observations The emf will start to increase in one direction Then when the magnet is out of the coil, the value will reach zero The emf will then increase in the other direction Secondly, explain these observations The magnet is moving through the coil This causes a change of flux linkage (cutting coil) The rate of change is proportional to value of emf The faster the magnet is moving, the higher the emf Alternating emf/current produced as the direction of flux linkage change is alternating Emf zero when magnet out of coil as the magnetic field is not cutting through the wire

Electromagnetic Induction in context: Microphones Microphones use electromagnetic induction to turn sound waves into electrical signals. Task: Copy down and use the diagram below to suggest how microphones achieve this function 5.1 x 10-10 N

Electromagnetic Induction in context: Speakers Loudspeakers turn specific electrical signals into specific sound waves Task: Using the diagram from before, suggest how loudspeakers and headphones might work! Hint: think the opposite! 5.1 x 10-10 N

Electromagnetic Induction on a large scale The world uses electromagnetic induction to convert or transmit current across long distances. When we generate electricity (e.g. in a generator attached to a turbine), it has to be converted before it can pass through to its destination (our homes). This is achieved using components called TRANSFORMERS. These are vital parts of a system that links power stations to our homes known as the NATIONAL GRID

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