P7: Magnetism & Electromagnetism Flashcards
What will happen when you place 2 like poles together?
They will repel
What will happen when you place 2 unlike poles together?
They will attract
What will the magnetic field of a permanent magnet be like?
Goes from north to south
How do you induce a temporary magnet?
By placing it inside of a magnetic field
What are magnetic metals?
- Iron
- Nickel
- Cobalt
What do you need to make an electromagnet?
- Battery
- Wire
- Iron core
What is an electromagnet?
An iron core with wire wrapped round it connected to a current
What happens when current is passed through the wire of an electromagnet?
Creates a magnetic field around the wire
This strongly magnetises the iron core, creating an electromagnet
How can you change the strength of an electromagnet?
- Change the current
- Coils around the iron core
What is Flemming’s left hand rule?
- First finger = magnetic field
- Second finger = current
- Thumb = movement of force
What are factors that can affect the size of the force?
- Changing current
- Changing strength of magnet
- Changing angle between wire and magnetic field lines
When is the greatest force produced?
When the wire is perpendicular with the magnetic field lines
When is the force 0?
When the wire and the magnetic field lines are parallel
What is the magnetic flux density and what is the equation for this?
- 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
What direction is the magnetic field in a simple electric motor?
North -> South
Which way is the current going in a simple electric motor?
Goes in a circuit from positive to negative
By south side, force goes down
By north side, force goes up
What happens as a result of the force going in different directions in a simple electric motor?
It will turn around
How does a moving coil loudspeaker work?
- 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
How does a moving coil microphone work?
- Sound makes diaphragm vibrate moving the coil
- Vibration causes coil to move back and forth past a magnet, generating a current
What is the generator effect?
Movement of a wire through a magnetic field produces a current
What is a transformer made up of?
- A soft iron core
- 2 sides with varying number of coils
What is the voltage like in a step up transformer?
Secondary voltage is greater than primary voltage
What is the voltage like in a step down transformer?
Secondary voltage is less than primary voltage
What are the transformer calculations?
- 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
