Magnetism and electromagnetism

Question 1

what is a magnetically soft magnet and why

Answer 1

Iron- because it loses its magnetism easily when it is removed from a magnetic field
-easily magnetised and demagnetised

Question 2

what is a magnetically hard magnet and why

Answer 2

Steel- since its domains are locked in place
not easily demagnetised

Question 3

what is the law of magnetism

Answer 3

• opposite poles attract
  -like poles repel

Question 4

What is a magnetic field

Answer 4

a region where a magnetic material experiences a force

Question 5

What does a magnetic line shows

Answer 5

the direction of the force that would act on a small N pole placed there

• show the strength of the field
  -show the size

Question 6

what are the two methods used for investigating the magnetic field

Answer 6

Iron Filings
A bar magnet and compass

Question 7

describe the method for using a compass to measure a magnetic field

Answer 7

1. Place plotting compass near the magnet on the piece of paper
2. place the compass on the edge of the north pole
3. once the compass has settled mark a dot where the north pole of the compass is pointing
4. Move the compass so that the south end is lined up with dot that you just plotted
5. one again place the north pole of the compass on the dot that you just plotted
6. repeat this process to reveal the magnetic field

Question 8

How do you create a uniform field

Answer 8

Place the bar magnets close together but not too close they move together

represented by parallel equally spaced lines

Question 9

How do you construct an electromagnet

Answer 9

iron core
wrap a coil wire round it
Pass a current through it

Question 10

what does an electrical current do to a conductor (wire)

Answer 10

Produces a magnetic field around it

electrical current in a conductor produces a magnetic field

direction of the current depends on the magnetic field

Question 11

How do you increase the force on a conductor

Answer 11

increase the amount of turns in the coil wire
Increase the current (by increasing the voltage and the power supply)
increasing the magnetic field

Question 12

how do you increase the strength of the magnetic field

Answer 12

by adding a magnetically soft iron core

Question 13

In a motor explain the motion of the coil of wire

Answer 13

• A wire carrying a current produces a circular magnetic field
• if this field is placed in a uniform magnetic field of a permanent magnet the two fields interact

-This exerts a force on the opposite sides of the coil in opposite directions.

• The coil starts to rotate

Question 14

explain how a loud speaker produces sound (with ac current)

Answer 14

-Current in the coil produces a magnetic field

• Field of coil interact with field of magnet
• Producing a force on cone
• Direction of current is constantly changing because current is AC (alternative current)
• Direction of magnetic field is continuously changing
• Direction of force changes
  (due to the charged particle movement not being parallel to the field )

-Cone vibrates

• Air particles (next to the cone) are made to vibrate

Question 15

How do you increase power in a motor

Answer 15

• Increase current through the coil
• Increase the strength of the magnetic field
• Increase the number of wires in the coil
• Increase the area of the coil (this increases the turning effect or moment)

Question 16

Describe how an electric bell works

Answer 16

• Switch is closed
• Current passes through circuit
• Electromagnet becomes magnetised
• This attracts the armature making the clapper hit the bell
• When the armature is no longer touching contacts, the circuit is broken
• So the electromagnet is no longer magnetic so armature is no longer attracted
• So armature springs back, reclosing circuit
• This cycle repeats creating the sound of an electric bell.