magnetism and em

Question 1

What are the magnetic materials

Answer 1

nickel
iron
cobalt
steels

Question 2

What are permanent magnets and where are they used

Answer 2

• Materials which are always magnetic and have set poles
• Compasses, speakers, generators, motors

Question 3

What are induced magnets and where are they used

Answer 3

• Magnetic materials become induced when they come in contact with a magnetic field. This causes them to create poles which will always attract the main magnet
• Used in electromagnets

Question 4

What is the shape and direction of a magnetic field

Answer 4

• Point from north to south
• Strength decreases further away, shown by less concentrated lines

Question 5

How do you use a plotting compass to determine magnetic field direction

Answer 5

Take the compass, keep it at any point on the magnetic field, see where it points, continue
- South points towards north pole of magnet

Question 6

How do we know the earth’s core is magnetic

Answer 6

• This is because compasses will always point to the geographic north and magnetic south pole of the earth.

Question 7

What does strenght of magnetic field depend on when created by a current

Answer 7

• Size of current
• distance from wire

Question 8

What is the magnetic field produced by a solenoid like

Answer 8

• Shape of bar magnet
• When a wire bends, the magnetic field joins to form a uniform line which passes through the centre
• This cancels out the magnetic field lines outside the solenoid , making them weaker because there are strong lines going through the centre

Question 9

What factors affect strength of field in a solenoid?

Answer 9

• Soft iron core used or not
• Number of coils
• Current

Question 10

What happens when you put a wire through a magnetic field?

Answer 10

• The wire has a magnetic field which interacts with the magnetic field of the magnet.
• This creates an equal and opposite force on the magnet

Question 11

What are magnetic forces caused by?

Answer 11

interactions between magnetic fields

Question 12

How does a motor work

Answer 12

• Make a wire into a coil
• One side gets pushed up, other gets pushed down
• Causes the ting to rotate
• Gets pushed the other way when reaching the other side

Question 13

How do generators produce energy in the small scale?

Answer 13

• Spin a coil of wire through a magnetic field
• Connect it to a sensitive ammeter which only shows milliamps
• Passing a wire through a magnetic field also produces a small voltage

Question 14

How do generators produce energy in large scale?

Answer 14

• Water heats up to form steam
• Steam spins the turbine
• Turbine spins the generator producing electricity

Question 15

What factors affect the size of the voltage induced with a generator?

Answer 15

• Speed of coil
• Size of coil
• Strength of magnetic field

Question 16

How do loudspeakers work?

Answer 16

• A coil of wire is wrapped around a pole of a magnet
• An alternating current gets pushed through this coil
• This then causes a magnetic field to be created by the wire
• Since there are interacting magnetic fields between permanent and the coil, a force acts upon the wire pushing it back and forth
• Wire connected to the cone
• Causes vibrations, create sound waves

Question 17

How do microphones work?

Answer 17

• Coil of wire inside microphone attached to the diaphragm
• Vibrations in sound cause the diaphragm to vibrate
• This causes the coil to move up and down, inducing a current due to the generator effect
• The current is taken out of the mic through a wire to a loudspeaker

Question 18

How is a voltage induced in a transformer?

Answer 18

• Current flows through primary coil
• It is alternating
• Since it has a current, it produces a magnetic field
• This interacts with the secondary coil
• Since the current is alternating, the magnetic field is changing and the coil interacting with a changing magnetic field induces a current due to the generator effect
• This current is also alternating