P15 - Electromagnetism
Independent learning
Introduction
In this chapter you will begin by reinforcing your knowledge of magnetism by looking at the magnetic fields around permanent magnets and how magnetism can be induced in some materials. You will then learn about the magnetic field produced by a current in a wire and investigate the factors that affect the direction and strength of this field. This will also include the field shape of a solenoid compared to the field around a simple bar magnet and the factors affecting the strength of an electromagnet. Separate science students will move on to describe how these devices can be used in a variety of devices.
Higher-tier students will learn about the motor effect, how a current carrying wire placed in a magnetic field experiences a force and how this effect can be used to create an electric motor. Separate science students will also cover the generator effect and the factors which affect the current induced in a wire as it is moved through a magnetic field. These concepts are applied to the design of a practical generator and the a.c. waveform produced as the coil in the generator rotates.
Separate science students also learn about the operation of a transformer in terms of changes in magnetic fields before constructing a practical transformer. The transformer equation will also be used to determine changes in potential difference along with a discussion of transformer efficiency and the application of transformers in the National Grid.
Specification links
Task 1: Know
Task 1a: Use look, cover, write check and quizlet to learn the answers to the core questions and the keywords for this topic. Make sure you click through the presentation to find the knowledge organiser(s) you need for your set because they are different for this topic:
Set 3 = Slide 1
Set 2 = Slide 2
Set 1 = Slides 2&3
Learn
Task 2: Magnetic fields
Task 2b: Make notes that:
Explain why a freely moving magnet will always come to rest along a North-South line
List the magnetic materials.
Define induced magnetism.
Describe the test for a magnet
Describe how to plot the field around a magnet using a plotting compass
Draw the magnetic field around a bar magnet, including arrows to show the direction of the magnetic field.
Task 2c: Complete the BBC Bitesize quiz
Task 2d: Complete and mark the exam questions
Task 3: Magnetic Fields of Electric Currents
Task 3c: Make notes that:
Describe how a current carrying wire has in induced magnetic field around it
Explain what the right-hand grip rule tells us and draw a diagram to help explain it.
Describe what a solenoid is and how the strength and direction of the magnetic field around it can be changed.
Draw and label a diagram to show the magnetic field inside and around a solenoid.
Describe how to construct a basic electromagnet and the different ways you can change the strength of an electromagnet.
Task 3d: Complete and mark the exam question
Set 2 go to task 5 now
Set 3 go to task 10 now
Task 4: Electromagnetic devices - Set 1 only
Task 4c: Make notes that:
Describe what a circuit breaker is.
Draw a labelled diagram of a circuit breaker and Explain how they work.
Describe what an electric bell is.
Draw a labelled diagram of an electric bell and Explain how they work.
Describe what a relay is.
Draw a labelled diagram of a relay and Explain how they work.
Task 4d: Complete and mark the exam question
Task 5: The Motor Effect - Set 1 & 2
Task 5a: Read throught the slides and the BBC Bitesize pages
Task 5c: Make notes that:
Define the motor effect
Describe two ways to reverse the direction a wire will move in due to the motor effect.
Explain what Fleming’s left-hand rule is, including what the first finger, second finger and thumb represent, include a Sketch to aid your explanation.
Define magnetic flux density and Give its unit.
Give the equation to calculate the size of the force that acts on a wire.
Describe the three ways to increase the size of the motor effect.
Explain how a DC motor works, including the role of the split-ring commutator
Draw and label a copy of the diagram on the right to help with your explanation.
Task 5d: Complete the BBC Bitesize quiz
Set 2 go to task 10 now
Set 1: Complete the checkpoint quiz
Task 6: The Generator Effect - Set 1 only
Task 6c: Make notes that:
Define the generator effect
Define electromagnetic induction
Draw a diagram to show how a potential difference can be induced in a wire.
Describe how you could increase the size of the induced potential difference and current.
Describe how you could reverse the direction of the induced current.
Task 6d: Complete and mark the exam question
Task 7: AC Generators - Set 1 only
Task 7a: Read through the slides and the BBC Bitesize page
Task 7b: Watch the videos
Task 7c: Make notes that:
Describe the difference between AC and DC
Describe what an alternator is.
Explain when the induced potential difference will be greatest and when it will be zero, in relation to the position of the coil. Use this diagram to help.
Describe 2 ways the potential difference produced could be increased.
Describe 2 ways in which the output would change if the coil rotated faster.
Explain what a DC dynamo is.
Draw the output potential difference graph from a DC dynamo.
Describe how a microphone works
Explain how a loudspeaker works
Task 7d: Complete and mark the exam question
Task 8: Transformers - Set 1 only
Task 8a: Read through the slides
Task 8c: Make notes that:
Describe what a transformer is, include “primary coil” and “secondary coil” in your description
Explain the difference between a step-up and a step-down transformer.
Draw and label a diagram of a step-up and and step-down transformer.
Write out the statements on the right, which describe how a transformer works, in the correct order
Give an example, other than the National Grid, where a transformer is used.
Task 8d: Complete and mark the exam question
Task 9: Transformer calculations - Set 1 only
Task 9a: Read through the slides
Task 9c: Make notes that:
Give the transformer equation in both word and symbol form.
Calculate the answer to the question on slide 14.
Explain what it means when we say that transformers are almost 100% efficient.
Explain why the power supplied to a transformer is equal to the power delivered by the transformer.
Give the symbol equation involving current and potential difference, which shows that power in = power out
Calculate the answer to the question on slide 20
Explain why electricity is transmitted through the National Grid at a high potential difference.
Task 10: Summary
Task 10a: Complete the Seneca units for this topic
Task 10b: Make a mind map or single page revision summary of this topic. Use the specification links to help you.