Magnetism Flashcards
What direction does magnetic field go
North to south
What is a magnetic field
Region where other magnets experience a force
What do compares do
Show magnetic field as are attracted to South Pole of magnet
Normally face north as earth has own field
What are permenant magnets
Magnets that produce own magnetic field
What are induced magnets
Magnetic material that become magnetic when in field eg iron or steel
When take away magnetic field quickly lose magnetism and stop making own field
What does the right hand thumb rule show
Moving current creates magnetic field
How does strength of field produced by a current change
With increases current or distance from wire
What is a solenoid
A coil of wire that produces a magnetic field
Increases strength of field produced by straight wire
Field lines look like bar magnet
How can the field strength of a solenoid be increased
Add iron core in coil
Iron becomes induced magnet when current flows
What is an electromagnet
A solenoid with iron core connected to a current, where the current can be turned on or off meaning that the magnetism of the magnet can be controlled
What are the two main uses of electromagnets
To move scrap metal, to pick up is turned on, to drop is turned off
Act as switches in circuits, when switch is closed electromagnet attracts iron contact which completed circuit, turning on motor
When does the motor effect occur
When a current carrying wire or conductor of current is put between magnetic poles,
the field around wire interacts with the magnetic field placed in, causes wire and conductor to exert force on each other, making one of them move
What condition does there have to be for the motor effect to occur
The wire or conductor must be at 90 degrees to the magnetic field
How can you increase strength of force felt in motor effect
Increase strength of magnetic field or increase current
What is magnetic flux density and what is it measured in
It is the amount of field lines in a region
Measures in Tesla’s (T)
What does each finger in Flemings left hand rule represent
Thumb is motion
First finger is field
Middle finger is current
How do electric motors work
Forces act on two side arms of a coil of wire carrying a current
Coil is on spindle and forces act one up one down causing it to rotate
Split ring commutator swaps contact every 1/2 turn to keep same rotating direction
How do loudspeakers work
AC through coil of wire attached to base of paper cone
Coil surrounds 1 pole of magnet and is surrounded by the their pole
Interaction of fields causes force on coil, so cone moves
Movement of cone causes sound waves as air vibrates
What does the generator effect do
Creates PD in a conductor, and also a current is conductor is part of complete circuit
How does the generator effect occur
Moving a magnet in a coil of core or moving conductor in a magnetic field
Shifting magnet from side to side creates blip in current
If move magnet in opposite direction Pd/current is reversed
So I’d keep moving magnet back and forth, AC current flows
How can you change the size of an induced PD through the generator effect
Increase speed of movement as cuts through more field lines
Increase strength of magnetic field so more lines to cut through
How do alternators create AC
Generators rotate coil in magnetic field (constructed like a motor)
As coil spins, current is induced in coil and it changes direction every 1/2 turn
Instead of split ring commutator, it has slip rings and brushes so contacts don’t swap, so AC is produced
How do dynamos create DC
Have split ring commutator instead of slip rings, so connection is swapped every half turn, so current flows same direction and direct current is produced
What is an oscilloscope
Graph that shows how generated PD is charged
