Magnetism Flashcards
What is electromagnetic induction?
The creation of a voltage (and maybe current) in a wire due to a change in magnetic field.
What is the generator effect?
When you move a wire in a magnetic field to produce a current. Or… When a magnet moves around a wire to produce a current.
How can I increase the voltage I get out of a dynamo/generator?
Increase the number of turns in the coil Increase the strength of the magnet Move the wire/magnet faster Reduce the gap between the wire and the magnet
How can I increase the current I get out of a generator?
Increase the number of turns in the coil Increase the strength of the magnet Move the wire/magnet faster Reduce the gap between the wire and the magnet
What is the energy transfer that occurs in a generator?
Kinetic energy -> Electrical energy
If I reverse the direction of the movement of a wire in a magnetic field, what happens to the current?
The current/voltage reverses too.
How does electromagnetic induction work?
When the coil/wire cuts the magnetic field lines… …a voltage is induced… …by electromagnetic induction
When I rotate a coil in a dynamo, at what part of the rotation is the biggest current/voltage induced?
When the coil is parallel to the magnetic field (because that’s when it cuts the most magnetic field lines)
Other than generating electricity, what are some uses for electromagnetic induction?
Detecting metal pipes and wires in walls.
As a generator coil turns around, where is the maximum voltage produced?
When the coil is perpendicular to the magnetic field
As a generator coil turns around, where is the minimum voltage produced?
When the coil is parallel to the magnetic field
If I move a wire in a magnetic field in a direction parallel to the magnetic field lines, why is no voltage produced?
No field lines are being cut by the wire.
How does electricity generation in a power station work, generally?
Boil some water, use it to rotate a coil in a magnetic field.
For most electricity generation, what type of current is produced?
AC
If I reverse the polarity of the magnets used in a generator, what happens to the current I induce?
It reverses.
If I reverse the magnets and the direction I rotate a generator coil, what happens to the current?
Nothing. It reverses twice, so it ends up the same.
What does a split ring commutator do in a DC motor?
Reverses the direction of the current every half term
How does a motor work?
- The current produces a magnetic field - This field interacts with the permenant field - Producing a force which turns the motor
What does each finger correspond to in Fleming’s Left Hand Rule?
Thumb = Force (F) Index = Magentic Field (B) Middle = Current (I)
How do I tell the strength of a magnetic field from its field lines?
The closer together they are, the bigger the magnetic field.
What is shown by the direction a field line points?
The direction the north pole of a compass would point when placed in the field.
When does a current carrying wire NOT produce a force in a magnetic field?
When the current is PARALLEL to the magnetic field
What is the wire in a motor made of and why?
Copper, because it’s a good conductor
What are the brushes on a DC motor made of
Carbon, because it’s a conductor and its hard wearing
What is a uniform field?
One where the field lines are parallel and evenly spaced
What direction do magnetic field lines always point?
From North to South
What is the motor effect?
When a current carrying wire is in a magnetic field, a force is produced.
Why does a current carrying wire in a magnetic field move?
- The current produces a magnetic field - This field interacts with the permenant field - Producing a force
Why do the coils of an electromagnet have to be insulated?
Otherwise the coils will short circuit and the current will not flow through the coils.
How does a loudspeaker work?
- The current produces a magnetic field - This field interacts with the permenant field - Producing a force which moves the cone
How do I set up a uniform magnetic field?
Two bar magnets with opposite poles close together, facing one another.
Describe an experiment I can do to see the magnetic field around a magnet?
- Place the magnet on a piece of paper
- Place a plotting compass at the end of a magnet
- Place an “x” at the point the compass points to.
- Place the compass so that the back end of the arrow touches the “x”. Place another “x” where the arrow is pointing.
- Repeat until you leave the page or you meet the magnet again
- Repeat the entire process again, starting at a different point.
