P7 magnetism and electro magnetism Flashcards
what is a permanent magnet
always magnetic and always have poles
what is an induced magnet
-materials that are magnetic but do not have a fixed pole
-can be made into temporary magnets if stroked by a permanent magnet
where does the direction always point
always point to the south pole away from the north pole
where do field lines point
from north to south
how do you find the direction of a currents magnetic field around a wire
right hand grip rule that goes round the wire
what are some characteristics of strong and weaker magnetic fields
-greater current
-greater distance from the wire the weaker the field
what are factors that effect the strength of a bar magnet
-size of current
-length
-cross sectional area
-number of coil turns
-using a soft iron core
what effect does a solenoid have on a magnetic field
It enhances the magnetic effect as coiling the wire causes the magnetic field to align and form a giant single field rather than lots of them all perpendicular to the direction of the current
what effect does an iron core have on a magnetic field
increases its strength as it is easier for magnetic field lines to
pass through than air
what is the motor effect
when the straight magnetic field of two magnets interacts with the circular magnetic field of a wire pushing the wire away from the field and the poles at 90 degrees
label flemings left hand rule
thumb= force
index= field
middle= current
how do electric motors work
-permanent magnets are in a fixed position
- In between a coil of current carrying wire is on an axis
-force on one side moves that side up
-force on other side moves that side down
what is electro magnetic induction
-when there is a movement between a conductor and a magnetic field a potential difference is created across the conductor
- This happens if the magnetic field changes as well
- A current flows if the conductor forms a complete circuit
- This current will produce its own magnetic field which oppose the change in movement
how does an electric generator work
-same setup as a motor with a coil of wire able to
rotate between two permanent magnets
- A turbine spins turning the coil of wire
- The movement of the wire causes the wire to
cut through the magnetic field
- It experiences a change in magnetic field
- This creates a potential difference
- If the coil of wire is connected to a complete
circuit an alternating current (AC) will flow
- Direct current current is produced
- This reverses the current each half-rotation so
current remains positive
– this system is called a dynamo
