Magnetism and Electromagnetism

Question 1

What are the two poles of a magnet?

Answer 1

North and South.

Question 2

How do these different poles of the magnet interact?

Answer 2

Like poles repel, unlike poles attract each other.

Question 3

What is a permanent magnet?

Answer 3

● A magnet that can produce its own magnetic field and will repel and attract other magnets when it is in contact with them
● It is made from a magnetic material
● It cannot be demagnetised

Question 4

Explain what a hard magnetic material is.

Answer 4

Hard magnetic materials get magnetised when an external magnetic field is applied and stay magnetised permanently when the external field is removed.

Question 5

Explain what a soft magnetic material is.

Answer 5

Soft magnetic materials get magnetised when an external magnetic field is applied but they get demagnetised (lose their magnetic field) when the external field is removed.

Question 6

Name four magnetic materials.

Answer 6

1. Iron
2. Cobalt
3. Nikel
4. Steel (Iron+Carbon)

Question 7

What is a magnetic field?

Answer 7

A region surrounding a magnet where other magnets will experience a force.

Question 8

Which direction do the field lines in a magnetic field point?

Answer 8

From north to south.

Question 9

Does a high concentration of field lines mean the field is strong or weak?

Answer 9

Strong

Question 10

True or false? - Magnetic field lines never cross each other.

Answer 10

True

Question 11

How can you produce a uniform magnetic field?

Answer 11

By placing opposite poles of two magnets across each other, you can create a uniform magnetic field where magnetic field lines are separated with a fixed distance between 2 magnets.

Question 12

How is a plotting compass used to map out a magnetic field?

Answer 12

● Place a compass (containing a needle magnet) on a piece of paper near the field
● Move the compass to different places on the paper
● Draw an arrow in each position in the same direction as the needle points
● Once you have gathered enough data, you can join the arrows to make a complete field pattern

Question 13

What must happen for a circular magnetic field to be created around a wire?

Answer 13

When current flows through a wire it induces a magnetic field.

Question 14

Use your hand to show Fleming’s Left Hand rule, stating which finger represent field quantity.

Answer 14

● Force (thumb)
● Magnetic field (index finger)
● Current (second finger)
● FBI

Question 15

What is the relationship (direction wise) between current, magnetic field and force?

Answer 15

They all act perpendicular to each other

Question 16

How can we increase the magnitude of the force acting on a current-carrying wire inside a magnetic field?

Answer 16

● Increase the size of the current
● Increase the strength of magnetic field (Use stronger magnet)

Question 17

What is the motor effect?

Answer 17

A current carrying wire is placed in a magnetic field and experiences a force that pushes the wire. The field from the current carrying wire interacts with the other magnetic field (the magnetic field it is placed in) so a force is applied on the wire. This force pushes the wire therefore the wire rotates.

Question 18

How do loudspeakers use current to work?

Answer 18

● A coil is placed inside a magnet
● An alternating current in this coil causes a magnetic field
● When the field interacts with the magnet, a force is produced (the motor effect)
● This force pushes and pulls the wire/cone of the speaker, causing it to move in different directions.
● Due to the alternating current, the force causes the cone to vibrate
● This causes pressure variations in the air (sound waves)

Question 19

How do microphones convert sound into electrical signals?

Answer 19

● When sound is produced, the pressure variations in the waves cause the diaphragm to vibrate
● A coil of wire is connected to the diaphragm, so as the diaphragm moves, so does the coil of wire
● The coil of wire is in a magnet so when it moves a voltage is induced in the coil
● As there is a complete circuit a current is also created

Question 20

If the current and the magnetic field are parallel to each other, which direction would the force act in?

Answer 20

No force will act when magnetic field is parallel to the current.

Question 21

How are electric motors kept rotating?

Answer 21

A commutator is used. This switches the current direction every half turn, which ensures that the coil keeps spinning.

Question 22

How do you produce an electric current using a magnet and a conductor on a small-scale?

Answer 22

• Moving a coil of wire into a magnet
• Or, moving a magnet into a coil of wire
• Once a voltage is induced, assuming there is a complete circuit, a current will also be induced.

Question 23

How is electrical current produced on a large-scale?

Answer 23

An electromagnet is rotated around a coil.

Question 24

What factors affect the size of an induced voltage?

Answer 24

● The number of turns on the coil of wire
● How strong the magnetic field is
● How fast you move the magnet

Question 25

How does a dynamo generate current?

Answer 25

A coil of wire rotates inside a magnetic field. A commutator is used to ensure it continues rotating in the same direction, therefore keeping the current flowing in the same direction (d.c. current).

Question 26

How is electromagnetic induction used in alternators to generate alternating current?

Answer 26

A coil of wire rotates in a magnetic field. The end of this coil is connected to slip rings which will cause the current to change direction while rotating. This means a.c is produced.