# Electromagnets.

In this worksheet, students will learn about the principles of Electromagnets and Solenoids as well as how they can be used in real life.

Key stage:  KS 4

Curriculum topic:  Physics: Magnetism and Electromagnestism

Curriculum subtopic:  Magnetic Fields

Difficulty level:

### QUESTION 1 of 10

Electromagnetism is the name we give to explain magic. Okay, so maybe not magic but it is dammed close! Using electromagnets we can literally make trains float above the track like in the MagLev train. Don't believe me? That's fine, I didn't when I was first told about this - but here's a video to prove it.

So - how on earth does this work? It's a set of complicated principles that allow electricity to make a magnetic field - and it's a principle that we make use of every day. 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 like with all fields, you can't see this, but you can see the effects of this. Here is a video showing you how a wire will be affected when a current (moving electrons) are passed through it.

Using that principle, 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 increasing the strength of the field around the wire.

This is what the field looks like when we make a solenoid:

By Goodphy - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=74899571

As you can see - this magnetic field now looks a lot like what you would find around a magnet - we're on our way to making something that will be able to lift a whole train into the air.

We can then improve this even further but putting an iron core into the coiled wire to improve the field even more.

The magnetic field around an electromagnet can be increased by increasing the current in the wire, making more loops with wire and 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 loses it 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.

Complete this sentence.

The 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 it into an electromagnet.

What is used to represent a magnetic field?

Triangles

Circles

Lines

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 compasses?

The fact that there are naturally occurring magnetic materials.

The fact that there is a magnetic force.

All of the above combined with the fact that the Earth has its own magnetic field.

Tick the four materials necessary to make a simple electromagnet.

Coiled wire

Magnetic force

Iron nail

Battery

Magnet

Wires

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 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.

Which type of magnetic materials is easier to magnetise?

 easy to magnetise stays magnetic after current is switched off hard (e.g. steel) soft (e.g. iron)

Give one benefit of using an electromagnet in a situation above 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

Complete this sentence.

The magnetic force is ___________.

invisible
EDDIE SAYS
The 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?

They will not be attracted to the magnet.
EDDIE SAYS
The iron filings are magnetic so they will be attracted to the 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 as there is no magnetic field at that point. Make sure you read the question and look out for words in bold that will try and trip you up.
• Question 3

What is used to represent a magnetic field?

Lines
EDDIE SAYS
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

Complete this sentence.

In an electromagnet, the number of coils________.

Increases the strength of the field.
EDDIE SAYS
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. If you think about it, more coils mean 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 means stronger magnet.
• Question 5

What led to the invention of compasses?

All of the above combined with the fact that the Earth has its own magnetic field.
EDDIE SAYS
The invention of compasses is due to the facts that there are naturally occurring magnetic materials along with the magnetic force produced by magnets, and that the Earth has its own magnetic field.
• Question 6

Tick the four materials necessary to make a simple electromagnet.

Coiled wire
Iron nail
Battery
Wires
EDDIE SAYS
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

Complete this sentence.

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

stronger
EDDIE SAYS
The magnetic field around an electromagnet becomes stronger when you make more loops around the wire. Think about the more coils, more electrons, more field thing we spoke about earlier.
• Question 8

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

Increase the electric current.
EDDIE SAYS
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.
• Question 9

Which type of magnetic materials is easier to magnetise?

 easy to magnetise stays magnetic after current is switched off hard (e.g. steel) soft (e.g. iron)
EDDIE SAYS
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 hard 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. You can easily drag Iron Man into a magnet and trap him there. Whereas when you do this with steel, it will stay magnetic afterwards and you couldn't drop Iron Man after the Hulk has beaten him up.
• Question 10

Give one benefit of using an electromagnet in a situation above a permanent magnet.