Magnetism and the Motor Effect Flashcards
Recall that…
Like poles repel
Opposite poles attract
Describe the uses of permanent magnets
Always magnetic, always have poles.
Used in speakers, compasses, and electric generators.
Explain induced magnets
Do not have fixed poles as magnetism must be induced.
These can be made into temporary magnets by stroking them with a permanent magnet.
This aligns all domains in the material in the same direction, creating a temporary magnet.
Electromagnets use temporary magnetic material in their core.
Describe the shape and direction of the magnetic field around bar magnets
Field lines point from North to South.
Field strength decreases with distance from the magnet.
Describe the use of plotting compasses to show the shape and direction of the field of a magnet
Plotting compasses are small compasses which show the direction and shape of a magnetic field at a given point.
Explain how the behaviour of a magnetic compass is related to evidence that the core of the Earth must be magnetic
The core is magnetic, and creates a large magnetic field around the Earth.
We know this because a freely suspended magnetic compass will align itself with the earth’s field lines and point North.
A compass is effectively a suspended Bar magnet, with its own north pole lining up with Earth’s North pole.
This cannot be right – like poles repel
So in fact, the Earth’s magnetic pole in the north is a magnetic South Pole and the geographic south pole is close to the magnetic North Pole.
Describe how to show that a current can create a magnetic effect around a long straight conductor
Current produces a magnetic field around a wire.
The direction is dictated by the right hand rule.
Strength of magnetic field strength:
Magnetic field strength depends on current size; Greater current, stronger magnetic field.
Strength also varies with distance from the conductor; Greater distance from wire’ weaker magnetic field.
Factors that affect the strength of magnetic field
Size of current
Length
Cross sectional area
Number of turns (coils)
Using a soft iron core
Explain what a solenoid is
Magnetic Field Shape is similar to a bar magnet.
Coiling the wire causes the field to align and form a giant single, almost uniform field along the centre of the solenoid.
Having an iron core in the centre increases its strength as its easier for magnetic field lines to pass through than air.
The fields from individual coils cancel inside to produce a weaker field outside the solenoid.
What happens when a current carrying conductor placed near a magnet
Wire with a current near a magnet:
The current produces a magnetic field, which interacts with the magnet’s field.
The force experienced on the conductor is equal and opposite to the force felt on the magnet.
Magnetic forces are felt due to the interaction between any two magnetic fields.
The magnetic field around the wire is circular, but the magnetic field between two magnets is straight.
Describe Fleming’s Left Hand Rule:
First Finger – Field (magnetic N to S)
Second Finger – Direction of current flow
Thumb – Direction of Force (motion)
Explain how the force on a conductor in a magnetic field is used to cause rotation in electric motors
A coil of wire in between two permanent magnets.
Current flows through the wire, and the magnetic field it produces interacts with the magnets.
One side of the coil gets forced down, the other side gets forced up.
This causes the coil to rotate.
Use the Left Hand rule to verify which side moves up or down.
