Albert Teen YOU ARE LEARNING:  Solenoids  # Solenoids ### Solenoids

Electromagnets are created by wrapping a current-carrying wire around an iron core. The shape of the coiled wire is called a solenoid.

In this lesson we will be looking at solenoids and their interesting properties. Out of the following options, what do you think might describe a solenoid? 1

Here we can see the magnetic field lines of a solenoid.

Remember that any current-carrying wire produces a magnetic field around it, in a direction which you can find by using the right hand thumb rule. 2

True or false: Each loop of wire in a solenoid produces its own magnetic field.  3

How can you find out the strength of a magnetic field by looking at the field lines?

A) The stronger the field, the further apart the lines. B) The stronger the field, the closer together the lines.  4

Each individual loop creates its own magnetic field. So if you increase the number of loops in a solenoid without making it longer, what will happen to the magnetic field?

A) The number of field lines will increase but stay the same width apart. B) The number of field lines will decrease but stay the same width apart.

C) The number of field lines will increase but become more closely packed.

Answer with A, B or C.  5

So if you increase the number of loops around a solenoid of a fixed length, the number of magnetic field lines will increase and become more densely packed. What does this mean for the magnetic field strength?

A) It increases B) It decreases C) It stays the same

Answer with A, B or C.  6

So a solenoid is a spiralled up current-carrying wire.

The strength of the magnetic field it produces depends on the number of coils of the solenoid. 1

Which solenoid produces the strongest magnetic field? Answer A or B.  2

The magnetic field lines in solenoid A are closer together because there are more of them.

The magnetic field lines of solenoid A would be very close together, indicating a strong magnetic field. 1

This diagram illustrates why solenoids are so useful. The magnetic fields of each loop add up to create the overall field lines show in the diagram. How does the magnetic field on the outside of the solenoid compare to the inside?

A) It is stronger B) It is weaker C) They are the same  2

The magnetic fields created by each individual loop of a solenoid add up to create this overall magnetic field.

We can see that the magnetic field inside the solenoid is really strong and uniform. All the lines are straight and parallel to one another. 3

Now, the shape of this magnetic field might remind you of something. What type of magnet does this magnetic field resemble?  We know that increasing the number of coils in a solenoid increases the magnetic field strength. There are also other ways we can change the field strength. What do you think happens if we place an iron bar inside the solenoid? The iron core's magnetic field can be turned on and off by switching the current through the wire on/off. So what do we call this iron core? So the iron core is an"induced magnet" which increases the magnetic field strength of the solenoid. Together, what do you think they are called? 1

When we place an iron core, such as an iron nail, inside a coil of wire it increases the strength of the magnetic field.

An electromagnet refers to the whole thing - a solenoid with an iron core inside it. 2

Iron is magnetic so when placed inside the magnetic field of the solenoid, it becomes an induced or temporary magnet.

This is very useful because we can switch the magnetic properties on and off by switching the current through the coil on/off. 