Paper 1 - Magnetism and Electromagnetism

Question 1

Describe how to use 2 permanent magnets to produce a uniform field line

Answer 1

• Position magnets parallel to each other on a sheet of paper
• Evenly and slowly sprinkle iron filings over the magnets
• Tap the surface of the paper to reveal the magnetic field lines

Question 2

What is the relationship between permanent and temporary magnets?

Answer 2

They always attract

Question 3

Describe the properties of magnetically soft substances

Answer 3

• Temporary magnets
• Only have a magnetic field line temporarily
• Need another magnetic field to become magnetic

Question 4

Describe the properties of magnetically hard substances

Answer 4

• Permanent magnets
• Always produce their own magnetic field

Question 5

What do unlike poles do?

Answer 5

Attract

Question 6

What do like poles do?

Answer 6

Repel

Question 7

What is the relationship between charge, current and time?

Answer 7

Q = It

Question 8

Give some disadvantges of underground electrical energy transmission

Answer 8

• Hard to set up
• Expensive to set up
• Hard to access

Question 8

How does current create sound waves in a loudspeaker?

Answer 8

• As the current passes through the coil, it generates a magnetic field
• The magnetic field from t he coil now interacts with the magnetic field from the permanent magnet
• These magnetic fields attract and repeal each other 50 times per second because a.c. is @ 50Hz
• This produces a resultant force on the cone
• This causes the cone to move in and our

Question 8

Give some disadvantages of overhead energy transmission

Answer 8

• Cannot be insulated
• Can be damaged by weather
• Visual pollution

Question 9

Give some advantages of underground electrical energy transmission

Answer 9

• Can be insulated
• Cannot be damaged by weather
• More reliable

Question 9

When is a voltage induced in a coil or conductor?

Answer 9

• When the voltage moves through a magnetic field
  or
• When a magnetic field changes through the voltage

Question 9

Give some advantages of overhead electrical energy transmission

Answer 9

• Easy to set up
• Cheap to set up
• Easy to access
• Minimal habitat disturbance

Question 10

What is a magnetic field line?

Answer 10

The region around a magnet where a force acts on another magnet or on a magnetic material

Question 11

What factors affect the size of the induced voltage?

Answer 11

• Strength of the magnet
• Speed at which magnetic field lines are cut
• Number of turns in the coil

Question 12

Describe the generation of electricity by the rotation of a magnet within a coil of wire

Answer 12

• Magnetic moves through a coil
• Magnetic field lines are cut by the coil
• Charged particles in the wire experience a force
• Which induced a voltage
• Whch generated electricity

Question 13

What happens when there is an electric current in a conductor?

Answer 13

A magnetic field is produced around it

Question 14

Describe how the force on a current-carrying conductor in a magnetic field changes with the magnitude and direction of the field and current

Answer 14

• If you increase the magnitude of the current through a wire or the size of the magnet being used, you increase the force on the wire.
• If you change the direction of the current or reverse the poles of the magnet, you change the direction of the force on the wire

Question 15

What is the purpose of the brushes in a d.c. motor?

Answer 15

The brushes provide a connection to the rotating commutator / coil

Question 16

What is the purpose of the commutator in a d.c. motor?

Answer 16

The commutator reverses the direction of the current once every half-turn

Question 17

What are some advantages of a thick wire?

Answer 17

• It reduces resistance
• A thin wire may melt
• A thin wire may bend

Question 18

What happens to the value for induced current when the polarity of the magnets is reversed?

Answer 18

• Becomes negative
• E.g. 2 mA becomes - 2 mA