Electromagnetism up to level 6

Question 1

State the two different poles of a magnet

How do the poles of a magnet interact with each other?

Answer 1

The poles of a magnet are the north pole and the south pole

Poles interact with each other becuase like poles repel and opposite poles attract

Question 2

What is induced magnetism?

What direction is the force caused by induced magnetism?

Which metals are magnetic?

Answer 2

Induced magnetism is when a metal becomes magnetic when it is placed near to a magnet

The force is always attractive. Both north poles and south poles will stick to metals

The magnetic metals are iron, nickel and cobalt

Question 3

Sketch the shape of the magnetic field around a bar magnet

Explain which direction magnetic field lines point in.

Answer 3

Magnetic field lines always point from north to south

Question 4

Explain two ways that you can investigate the field lines around a bar magnet

Answer 4

One way to investigate the field lines round a bar magnet is to sprinkle iron filings around the magnet. The filings should line up so that they are lying along the magnetic field lines.

Another way to investigate field lines is to use a plotting compass. Place the compass next to the magnet and draw a dot where the pointer is pointing to. Then move the compass onto the dot and draw the dot where the pointer is pointing to now. Repeat the process until you have returned at the magnet.

Question 5

Describe the magnetic field around the earth

Answer 5

The magnetic field has the same shape as a bar magnet. It has a south pole at the geographical north pole and a north ple at the geographical south pole

Question 6

Describe the shape of the magnetic field around a current carrying wire

Answer 6

A current carrying wire has a circular magnetic field around it

Question 7

Explain how to find the direction of the magnetic field around a current carrying wire

Answer 7

Use the right hand grip rule. Place your thumb in the direction of the current and the magnetic field goes in the direction that your fingers curl in

Question 8

What is the effect on the magnetic field around a wire if:

a) the size of the current is increased
b) the direction of the current is reversed

Answer 8

a) If the size of the current is increased then the strength of the magnetic field lines increases. This can be represented as there being more magnetic field lines so they are closer together.
b) If the direction of the current is reversed then the current will circle in the opposite direction around the wire

Question 9

Describe the magnetic field produced by a soleniod

Answer 9

The magnetic field around the outside of a solenoid appear the same as a bar magnet. The field inside the solenoid is uniform (the field lines are parallel) and strong (the field lines are close together)

Question 10

State some uses of electromagnets

Answer 10

The can be used in:

Bells to move the hammer

Locks to open and close the lock

Circuit breakers to break the circuit if the current gets to high

In recycling plants to seperate out magnetic and non-magnetic metals

Question 11

What is the structure of an electromagnet

Answer 11

An electromagnet is made of a coil of wire (a solenoid) wrapped around an iron core

Question 12

Which factors increase the strength of an electromagnet

Answer 12

Increase the number of turns of wire around the iron core

Increase the size of the current passing through the wire

Question 13

Describe how to investigate the effect that changing the current has on the strength of an electromagnet

Answer 13

1. Set up the equipment as shown in the diagram
2. Set the current to 1 A and add paperclips to the end.
3. Record the maximum number of paperclips that the electromagnet can hold
4. Increase the current to 1.5A and record the number of paperclips that it can hold
5. Repeat the experiment a further 3 times, increasing the current by 0.5A each time and recording the number of paperclips that it can hold
6. Plot a graph of number of paperclips (x-axis) against current (y-axis)

Question 14

Descirbe what happens to a current carrying wire when it is perpendicular to a magnetic field

What happens if the size of the current is increased?

What happens if the size of the force is increased?

Answer 14

The wire will feel a force that is perpendicular to both the current and the magnetic field

If the size of the current is increased the size of the force will increase.

If the size of the magnetic field is increased, the size of the force will also increase

Question 15

Explain how to calculate the size of the force on a current carrying wire

Example: what is the force on a 2cm length of wire carrying a 3A current perpendicular to a 0.25T magnetic field?

Answer 15

To find the force on a current carrying wire use this equation:

F = BIL

F = force (N - newtons)

B = magnetic field strength (T - Tesla)

I = Current (A - Amps)

L = length (m - meters)

Example:

first convert the length into metres: 2cm = 0.02m

F = BIL

= 0.25 x 0.02 x 3

= 0.015N