Science 8th grade
UNIT 13: Magnetism 13.5 A stronger electromagnets
Science 8th grade
UNIT 13: Magnetism 13.5 A stronger electromagnets
Electromagnets have many different uses.
• They are used in electric motors and generators.
• They are used in doorbells and in electric switches called relays.
An engineer needs to be able to design an electromagnet which has just the right strength for a particular job.
Making a stronger electromagnet
We have already seen one important way to make an electromagnet stronger - add an iron core. Here are two other ways:
• Make a coil with more turns of wire.
The picture shows a coil with more turns of wire. The wire is longer and so, as the electric current flows through it, it makes a stronger magnetic field.
• Make a bigger electric current flow in the coil of wire. Connect two batteries to the coil, instead of one. This will make a bigger electric current flow so that the magnetic field will be stronger. (The batteries must be connected end-to-end, as shown.)
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Measuring electric current
If you use two batteries instead of one, the current in the electromagnet will be twice as great.
You may be able to use an instrument called an ammeter to measure the current flowing in the coil. Electric current is measured in units called amps, symbol A.
If you use a low-voltage power supply instead of batteries, you will be able to adjust it to control the value of the current.
Question
1) Mia makes two electromagnets, one with 10 turns and the other with 20 turns. She connects the first one to a single battery and the second one to two batteries. Mia finds that the second electromagnet is stronger than the first. She says, "This shows that more turns and more current make a stronger electromagnet.'
a: Explain why Mia cannot be sure that her conclusion is correct.
b: Describe how she should alter her experiment to make it a fair test.
Activity 13.5 (Improving an electromagnet)
SE: You are going to investigate whether some ideas are correct or not by constructing a fair test.
You have already learnt how to make an electromagnet by winding a coil of wire around a nail and how to test the electromagnet using paperclips.
In this investigation, your task is to test two ideas:
• An electromagnet is stronger if it has more turns of wire.
• An electromagnet is stronger if the electric current flowing through it is greater.
Plan your investigation. Check your ideas with your teacher before you carry them out. Remember - you must only change one factor at a time.