Unit 7 - Magnetism and Electromagnetism Flashcards
What is the difference between permanent magnets and induced magnets?
Magnets that always produce a magnetic field, whereas induced magnets become magnetised when in another magnetic field
Which metals are magnetic?
Iron nickel and cobalt are attracted to permanent magnets
What is the motor effect?
A wire carrying a current in a magnetic field will experience a force by producing its own magnetic field that interacts with the other. Only works if current and magnetic field lines are perpendicular, if wire is parallel no force is experienced
What is the right hand rule?
Shows the direction of current and magnetic field. Hold right hand out in a thumbs up shape. The direction of the thumb is the direction of current and the direction of the fingers is the direction of the magnetic field
What is Fleming’s left hand rule?
Gives direction of force:
Thumb = force
First finger = field
Middle finger - current
How do motors work?
Using the motor effect: both sides of a coil experience a force in opposite direction causing it to turn. However the current must be reversed at every half turn to keep the coil spinning, which is why we use split ring commutators
How can we increase the speed in a motor?
-Increase current
-Add more turns to the coil
-Use a stronger magnet
How do loudspeakers work?
Using the motor effect: a current is sent from a source (eg phone) causing the coil and speaker cone to vibrate as a result of varying current to produce sound waves
What is the generator effect?
A generator induces an alternating P.D in a spinning coil in a magnetic field (requires slip rings but not split rings). Without a split ring, the output is an A.C (alternating current)
How can we increase the output of a generator?
-Add more turns to the coil
-Use stronger magnet
-Turn faster (requires more energy)
What is the difference between what dynamos and generators produce?
Dynamos produce D.C
Generators produce A.C
How does a microphone work?
‘Inverted’ loudspeaker. Sound waves cause the coil to oscillate past the magnet which induces a signal
What do transformers do?
Change the transition voltage through national grid to reduce energy lost as heat due to resistance of cables
What does a step-up transformer do?
Increases voltage and decreases current, as V and I are inversely proportional
How is electricity wirelessly transmitted from one coil to another?
A.C in the primary coil induces an alternating magnetic field in the soft iron core (iron is easily magnetised and demagnetised). This magnetic field induces a current/voltage in the secondary coil. We use A.C as D.C would create a static magnetic field, which wouldn’t induce a current
