Magnets And Electromagnets

Question 1

What is repulsion?

Answer 1

If the poles are the same they repel

Question 2

What is attraction?

Answer 2

If the poles are opposite they attract

Question 3

Is magnetism a contact force?

Answer 3

No

Question 4

What is the force between a magnet and a magnetic material?

Answer 4

Attractive

Question 5

What are the magnetic materials?

Answer 5

Iron, cobalt, nickel, steel

Question 6

What is a permanent magnet?

Answer 6

Produces its own magnetic field which is always there

Question 7

What is an induced magnet?

Answer 7

On object that becomes magnetic when it is placed within a magnetic field

Question 8

What is the force between an induced magnet and a permanent magnet?

Answer 8

Always attractive

Question 9

What happens if an induced magnet is removed from the magnetic field?

Answer 9

It will quickly lose most or all of its magnetism

Question 10

What is a magnetic field?

Answer 10

The region around a magnet where another magnet or magnetic material will experience a force due to the magnet
Represented by magnetic field lines which show the direction of the force that would act on a North Pole at that point, pointing from north to south
Field strength is greatest at the poles
The closer together the field lines, the stronger the field

Question 11

How do you plot a magnetic field?

Answer 11

Small compases placed around a bar magnet will point in the direction of the field lines
If not near a magnet, the compass will align with Earths magnetic field
As a compass points towards a South Pole, the magnetic pole near the Earths geographic North Pole is actually a south pole

Question 12

What is electromagnetism?

Answer 12

If an electric current flows through a wire, it will produce a magnetic field around the wire
The field strength increases with greater current and closer to the wire
Reversing current reverses the direction of the field
The field around a wire takes the shape of concentric circles at right angles to the wire
Fingers curl in direction of magnetic field if thumb points in the direction of the current

Question 13

What is a solenoid?

Answer 13

Cylindrical coil of wire
Bending a current carrying wire into a solenoid increases the strength of the magnetic field
The shape of the magnetic field is similar to that of a bar magnet
Inside the solenoid, the magnetic field is strong and uniform which means it ah the same strength and direction at all points
Electromagnets are often solenoids with an iron core

Question 14

What are advantages of electromagnets?

Answer 14

Turned on and off
Strength can be increased or decreased by adjusting current

Question 15

What is a scrap yard cane?

Answer 15

Heavy objects containing magnetic materials can be lifted using an electromagnet

Question 16

How does an electric bell operate?

Answer 16

Switch is pressed to turn electromagnetic on
The iron armature is attracted towards the electromagnet, making the hammer strike the gong
The circuit is broken so the the electromagnet stops working and the armature springs back
Circuit is complete again and the cycle starts again when the switch is pressed

Question 17

What is a circuit breaker?

Answer 17

The circuit is held closed by a spring, but if the current becomes too large the electromagnet becomes strong and pulls the switch into an open position to turn the current off

Question 18

What is the motor effect?

Answer 18

When a current carrying wire is placed in a magnetic field, it experiences a force
The force is due to the interaction between the field created by the current in the wire and the magnetic field in which the wire is placed
The magnet producing the field will experience an equal sized force in the opposite direction
The direction of the force is reversed if current or magnetic field are reversed

Question 19

What is Flemings left hand rule?

Answer 19

Thumb is motion
First finger is field
Second finger is current

Question 20

What is magnetic flux density?

Answer 20

A measure of the strength of a magnetic field
F = BIl
B is magnetic flux density in Tesla

Question 21

What is an electric motor?

Answer 21

A current carrying coil of wire in a magnetic field tends to rotate
Each side of the coil experiences a force due to being a current carrying conductor in a magnetic field
The forces on each side of the coil are in opposite directions

Question 22

What does the split ring commutator do?

Answer 22

Keeps the motor spinning in the same direction by swapping contacts with the power supply every half turn so current always flows in the same direction relative to the magnetic field.
Faster by increasing current or magnetic field strength
Reverse current or magnetic field

Question 23

How do loudspeakers work?

Answer 23

Motor effect converts changes of currents in a coil of wire to changes of pressure in sound waves
A coil of wire is placed inside a permanent magnet and is attached to a diaphragm
When a current flows through the coil it experiences a force due to the motor effect
This causes the diaphragm to move
When the current changes direction, the force on the coils also changes direction, causing the diaphragm to move in the opposite direction
Variations make the coil and diaphragm vibrate
These vibrations create variations of pressure in air which form a sound wave
The frequency of sound wave is the same as the frequency of the ac supplied

Question 24

Lenz’s Law

Answer 24

The induced potential difference always opposes the change that produces it. The coil will apply a force to oppose the magnet being pulled away from the coil. Therefore, the end of the coil closest to the magnet will become a south pole. This means it will attract the north pole of the magnet.