P7: Magnetism & Electromagnetism

Question 1

What will happen when you place 2 like poles together?

Answer 1

They will repel

Question 2

What will happen when you place 2 unlike poles together?

Answer 2

They will attract

Question 3

What will the magnetic field of a permanent magnet be like?

Answer 3

Goes from north to south

Question 4

How do you induce a temporary magnet?

Answer 4

By placing it inside of a magnetic field

Question 5

What are magnetic metals?

Answer 5

• Iron
• Nickel
• Cobalt

Question 6

What do you need to make an electromagnet?

Answer 6

• Battery
• Wire
• Iron core

Question 7

What is an electromagnet?

Answer 7

An iron core with wire wrapped round it connected to a current

Question 8

What happens when current is passed through the wire of an electromagnet?

Answer 8

Creates a magnetic field around the wire
This strongly magnetises the iron core, creating an electromagnet

Question 9

How can you change the strength of an electromagnet?

Answer 9

• Change the current
• Coils around the iron core

Question 9

What is Flemming’s left hand rule?

Answer 9

• First finger = magnetic field
• Second finger = current
• Thumb = movement of force

Question 10

What are factors that can affect the size of the force?

Answer 10

• Changing current
• Changing strength of magnet
• Changing angle between wire and magnetic field lines

Question 11

When is the greatest force produced?

Answer 11

When the wire is perpendicular with the magnetic field lines

Question 12

When is the force 0?

Answer 12

When the wire and the magnetic field lines are parallel

Question 13

What is the magnetic flux density and what is the equation for this?

Answer 13

• Amount of magnetic flux in a certain area
• Force(N) = Magnetic flux density(T) x current(A) x length(m)
• F = B x I x l

Question 14

What direction is the magnetic field in a simple electric motor?

Answer 14

North -> South

Question 15

Which way is the current going in a simple electric motor?

Answer 15

Goes in a circuit from positive to negative
By south side, force goes down
By north side, force goes up

Question 16

What happens as a result of the force going in different directions in a simple electric motor?

Answer 16

It will turn around

Question 17

How does a moving coil loudspeaker work?

Answer 17

• By making a diaphragm attached to a coil vibrate
• Current is passed through coil, this generates force
• Each change in direction causes a change in vibration in the diaphragm

Question 18

How does a moving coil microphone work?

Answer 18

• Sound makes diaphragm vibrate moving the coil
• Vibration causes coil to move back and forth past a magnet, generating a current

Question 19

What is the generator effect?

Answer 19

Movement of a wire through a magnetic field produces a current

Question 20

What is a transformer made up of?

Answer 20

• A soft iron core
• 2 sides with varying number of coils

Question 21

What is the voltage like in a step up transformer?

Answer 21

Secondary voltage is greater than primary voltage

Question 22

What is the voltage like in a step down transformer?

Answer 22

Secondary voltage is less than primary voltage

Question 23

What are the transformer calculations?

Answer 23

• Vp/Vs(V)= np/ns
• Vs x Is = Vp x Ip
• Vp = voltage in primary coil
• Vs = voltage in secondary coil
• np = number of turns in primary coil
• ns = number of turns in secondary coil
• Ip = current in primary coil
• Is = current in secondary coil