Chapter 12 - Electromagnetism Flashcards
Which way do the magnetic waves travel in a magnetic field ?
From North to south
How can you increase the strength of a magnetic field ?
- increase the number of turns in the coil
- increase the current through the coil
What is a long coil of wire referred to as ?
solenoid (a long coil with many turns)
What feature does a magnetic field produce by a solenoid have ?
-the shape of the field is similar to that around a bar magnet and there are magnetic fields around the poles of the solenoid
How do you carry out the right hand grip rule and what does it help you to show ?
- helps to show which way the poles are around on the solenoid
- grip the solenoid with your fingers going the way of conventional current. Your thumb will point towards the north pole.
What happens when the direction of current changes in a wire ?
The polarity of the magnet is reversed, then the direction of the force on the wire is reversed.
What does each finger in Fleming’s left hand rule show us ?
Thumb - direction of the force
Index finger - direction of the field
second finger - direction of the current
Name two devices that use the fact that there is a force on a current-carrying wire .
loudspeakers and electric motors
How can the turning affect on a coil be increased ?
- increasing the current in the coil
- increasing the number of turns in the coil
- increasing the strength of the magnetic field
- increasing the area of the coil
What does the graph of voltage against time look like for a dc circuit ?
A constant straight line
What does the graph of voltage against time look like for a ac circuit ?
Regular waves from +325v to -325v
What’s the definition of electromagnetic induction ?
Producing an electrical voltage by charging the magnetic field near a conductor
Who discovered induction ?
Michael Faraday
How would you demonstrate EMI ?
passing a magnet through a coil of wire and placing a centre zero ammeter to measure the current
What conditions do the magnet and solenoid need to have to a) create a current b) create no current
a) - one or the other has to be moving
b) - when they both are stationary
How can you increase the size of the induced current in EMI ?
- moving the magnet faster
- using a stronger magnet
- using a coil with a greater amount of turns
What did Faraday conclude from his iron ring experiment ?
- Closing the switch caused an increase in the current in the right-hand coil.
- this caused an increased magnetic field in the RH coil
- since the iron core links the coils magnetically the magnetic field is also increased on the LH coil
- this cause increased current to flow through the ammeter
What is the other name for an a.c. generator ?
an alternator
Look at the graph on page 176
It could be a potential Q !!!!
How can you increase the size of the induced voltage of in an a.c generator ?
- rotating the coil faster
- using stronger magnets
- using a coil with more turns
- wrapping the coil around a soft iron core
How many coils does a step up transformer have in it’s primary and secondary coils ?
Less in its primary. More in its secondary.
How many coils does a step down transformer have in it’s primary and secondary coils ?
More in its primary. Less in its secondary
What are the three parts all transformers have ?
- primary coil (Vp)
- secondary coil (Vs)
- laminated iron core
What is the transformer equation ?
Ns / Np = Vs / Vp
