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Understand Electromagnets

Worksheet Overview

QUESTION 1 of 10

Electromagnetism is the name we give to explain magic. Okay, so maybe not magic but it is very close! Using electromagnets, we can literally make trains float above the track like in the MagLev train. Sounds hard to believe, doesn't it!

So, how on earth does this work? It's a set of complicated principles that allow electricity to make a magnetic field.  What's more, we make use of this principle in everyday life! Maybe not in such a big and dramatic way as the MagLev train, but it's inside nearly all of our electronic equipment. 

 

The thing is that electric currents (moving electrons) have magnetic fields around them. A straight wire carrying electricity has a circular magnetic field around it, whereas a coil of wire has a magnetic field in the same shape as a magnet. Just as with all fields, you can't see this, but you can see the effects of it. 

 

It is easy to make a simple electromagnet - we just take the wire and make it into a coil. This is called a solenoid and has the effect of increasing the strength of the field around the wire.

 

We can then improve the field even further by putting an iron core into the coiled wire. 

 

A battery is connected to a wire. The wire is then wrapped around an iron nail.

 

The magnetic field around an electromagnet can be increased by increasing the current in the wire, making more loops with wire and by placing an iron or steel core inside the wire, as shown in the diagram above.

Iron is magnetically soft, so it is easy to magnetise and it loses its magnetism when the electric current is turned off. Steel is magnetically hard, which makes it hard to magnetise, but it stays magnetic after the current is switched off.

 

Right then, are you ready to have a go at some questions on this subject?

Which of the options below will complete this sentence?

 

A magnetic force is ___________.

Visible

Invisible

What will happen if you place iron filings around an electromagnet without a current? 

They will repel the magnet

They will not be attracted to the magnet

They will form the magnetic field around the magnet

They will turn into an electromagnet

What is used to represent a magnetic field?

Triangles

Circles

Lines

Which of the options below would complete this sentence?

 

In an electromagnet, the number of coils ________.

Increases the current

Increases the strength of the field

What led to the invention of the compass?

The fact that there are naturally occurring magnetic materials

The fact that there is a magnetic force

Both of the above, combined with the fact that the Earth has its own magnetic field

Tick the materials necessary to make a simple electromagnet.

Coiled wire

Magnetic force

Iron nail

Battery

Magnet

Wires

Which of the options below can be used to complete this sentence?

 

An electromagnet has 10 loops coiled around it. A pupil makes another 10 loops. The magnetic field is now __________.

Stronger

Weaker

Following on from the previous question, tick another way the magnetic field around an electromagnet can be increased.

Make more loops

Increase the length of the wire

Increase the electric current

Fill in the table below for the two types of magnetic material.

 Easy to MagnetiseStays Magnetic After Current is Switched Off
Hard (e.g. steel)
Soft (e.g. iron)

Give one benefit of using an electromagnet in a situation, rather than a permanent magnet.

An electromagnet will pick up all types of metal

A permanent magnet will only pick up magnetic materials

You can turn an electromagnet off and it will lose its magnetism

  • Question 1

Which of the options below will complete this sentence?

 

A magnetic force is ___________.

CORRECT ANSWER
Invisible
EDDIE SAYS
That's the first question under your belt - how did you get on with it? A magnetic force is invisible - we cannot see it, we can only see its effects. We can draw the force around a magnet (both permanent and electromagnetic) using lines and arrows. How close the lines are together tells you how strong the force is and the arrows represent the direction of the force.
  • Question 2

What will happen if you place iron filings around an electromagnet without a current? 

CORRECT ANSWER
They will not be attracted to the magnet
EDDIE SAYS
Did this one catch you out because you thought there must be more than one correct answer? It was a bit of a tricksy question, but in fact there was only the one correct answer - option two. Iron filings are magnetic so they will be attracted to a magnet and they will also take the shape of the magnetic field around the magnet. However, when you do not have a current going through an electromagnet, this will not happen since there is no magnetic field at that point. Make sure you read the question carefully and look out for words in bold that may try and trip you up.
  • Question 3

What is used to represent a magnetic field?

CORRECT ANSWER
Lines
EDDIE SAYS
Have you ever been asked to draw the magnetic field of a magnet? It may have been a year or two ago but cast your mind back to how you did it. Magnetic fields are represented using lines. As we have said in a previous question, how close the lines are together shows you how strong the field is, and the arrows on the lines show you the direction of the field.
  • Question 4

Which of the options below would complete this sentence?

 

In an electromagnet, the number of coils ________.

CORRECT ANSWER
Increases the strength of the field
EDDIE SAYS
What did you make of this one - a bit tricky, maybe? Both the options look like reasonable choices, don't they? However, if you think about it, having more coils isn't going to affect how much current is flowing through them. So the correct answer must be the second option. There are a few things that will affect the field strength: the current (how many electrons there are making a field); the iron core (different types of metal will work better than others); and the number of coils. More coils means there is more wire in the same amount of space. What do the electrons travel through? The wires, so if there are more wires, then there must also be more electrons. What causes the magnetic field? Moving electrons - so more coils means more electrons, which in turn means a stronger magnet.
  • Question 5

What led to the invention of the compass?

CORRECT ANSWER
Both of the above, combined with the fact that the Earth has its own magnetic field
EDDIE SAYS
Oh this was a bit confusing, wasn't it? Here's an example of how important it is to read through to the end of a question! You could have ticked either of the first two options and not been wrong, just not given the whole picture. The invention of the compass was due to several factors: that there are naturally occurring magnetic materials; there is a magnetic force produced by magnets; and that the Earth has its own magnetic field.
  • Question 6

Tick the materials necessary to make a simple electromagnet.

CORRECT ANSWER
Coiled wire
Iron nail
Battery
Wires
EDDIE SAYS
You needed to tick four answers for this question. Did you get them all? A simple electromagnet can be made using coiled wire around an iron nail, connecting wires and a battery. All you need is some store of energy, something that electrons can move easily through and something to help the magnetic field on its way.
  • Question 7

Which of the options below can be used to complete this sentence?

 

An electromagnet has 10 loops coiled around it. A pupil makes another 10 loops. The magnetic field is now __________.

CORRECT ANSWER
Stronger
EDDIE SAYS
Don't worry if you weren't sure about this one - you can always go back to the Introduction and read about the electromagnet once more to help to get things sorted in your mind. The magnetic field around an electromagnet becomes stronger when you make more loops around the wire. Remember the more coils, more electrons, more field thing we spoke about earlier!
  • Question 8

Following on from the previous question, tick another way the magnetic field around an electromagnet can be increased.

CORRECT ANSWER
Increase the electric current
EDDIE SAYS
Did you get this one? Apart from making more loops around the iron core, the strength of an electromagnet can be increased by increasing the electric current. Again, moving electrons are the things that make stuff magnetic, so if you increase the number of electrons by increasing the current, you're going to increase the magnetic field strength. Got it?!
  • Question 9

Fill in the table below for the two types of magnetic material.

CORRECT ANSWER
 Easy to MagnetiseStays Magnetic After Current is Switched Off
Hard (e.g. steel)
Soft (e.g. iron)
EDDIE SAYS
Another one that you need to try to learn. Well done if you got it correct. Iron is magnetically soft, so it is easy to magnetise and loses it magnetism when the electric current is turned off.
Steel is magnetically hard, which makes it difficult to magnetise but it stays magnetic after the current is switched off. This is why we use iron in electromagnets because we want to be able to turn them off and for them to lose their magnetism.
  • Question 10

Give one benefit of using an electromagnet in a situation, rather than a permanent magnet.

CORRECT ANSWER
You can turn an electromagnet off and it will lose its magnetism
EDDIE SAYS
We have a trick answer in here - option two is correct, but is not a reason to choose a permanent magnet because this applies to both permanent and electromagnets. The first answer is just rubbish - we all know that! Read over the question carefully and look for the one that applies in the situation you are given. One place where an electromagnet is better than a permanent one is at a car dump - it is necessary to be able to both pick up steel cars using some type of a magnet and also to drop them - an electromagnet is perfect for this task! Brilliant effort! You've completed this activity and hopefully moved one step nearer to conquering that physics. Well done for all that hard work.
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