Magnetsism And Electromagnestism Flashcards
Information about magnets and magnetic fields
All magnets have two poles-North and South- produce a magentic field- travels from north to south
Closer the lines the greater the magnetic field
Magnetic field strongest at the poles
Forces between a magnet and magnetic material always attractive- like poles repel/unlike poles attrcat
How do compasses show direction of magnetic fields
Tiny bar magnet inside compass.
The N pole is attracted to the South pole of any magnet it is near. It point in the direction of the magnetic field it is in
When not near a magnet a compass always points North. Earth generates its own magnetic field, Earth must be magnetic
What are permanent magnets
Magnets that produce their own magnetic field
Always attractive with induced
What are induced magnets
Magnetic material that turn into a magnet when put into a magnetic field
Always attractive with permanent
When you take away the magnetic field, induced magnets lose their magnetis and stop producing a magnetic field
How does a moving charge create a magnetic field and how can it be recorded
1)Current flows through a wire, a magnetic field is created around the wire
2)Field is made up of concentric circles perpendicular to the wire, wires in the centre
3)A compass will trace the direction of the magnetic field (current being carried)
4)Changing direction of current will change the direction of the magnetic field-use the right hand thumb rule to see which way it goes (point your thumb to the direction of current and curl your fingers. Direction of finger =direction of the field
5) Strength of the magnetic field produced changes with the current and the distance from the wire. The larger the current through the wire, of the closer to the wire you are, the stronger the field
How to increase strength of magnetic field produced by a wire, how are magnetic fields like in solenoids
1) Wrap wire into a coil called a solenoid to increase strength of magnetic field because field lines around each loop of wire line up with each other
2) Field lines point in the same direction that are very close to each other. Magnetic field in a selonoid is strong and uniform same strength and direction at every point, outside the coil magnetic field is like a bar magnet has a N and S side.
3) Increase field strength of selonoid by putting a block of iron in the centre of the coil-iron core becomes induced. If the current is stopped, the magnetic field disappears
How is the motor effect caused
Current carrying a wire is put between magnetic poles, the magnetic field around the wire interacts with the magnetic field it has been placed in. Both the magnet and conductor exert a force on each other (motor effect)
How to find a size of a force
Force = Magnetic flux density X current x length
How to find direction of force using the left hand rule
1)Use your left hand, point your first finger in the direction of the magnetic field
2)Point your second finger in the direction of the current
3)Thumb will then point in the direction of the force (motion)
4)Current or magnetic field is reversed, direction of force will also be reversed- used as motors
How to use the right hand thumb rule
Use your right hand , point your thumb in the direction of the current and curl your fingers.
Direction of fingers is the directiom of the field
How to experience full force in a magnetic field
1) To experience full force, the wire has to be 90° at the magnetic field. The wire runs parallel to the magnetic field, no force experienced. Angles inbetween feel force.
2) The force always act at right angles to the magnetic field of teh magnets and the direction of the curren of the wire.
3) Apply a current to a set of rails inside a horseshoe magnet. Bar is placed on the rails, circuit completed. Force rolls the bar along the rails
4)The magnitude of the force increases with the strength of the magnetic field
5) Force imcreases with the amount of current passing through the conductor
Force acting on a conductor depends on three things:
Magnetic flux density- how many field lines there are in a region-shows strength of magnetic field
Current- size of the current
Length- length of conductor in magnetic field
How does a current carrying coil rotate in a magnetic field
1) Forces act on the two sides of a coil of wire thats carrying a current.These are usual forces which act on any current in a magnetic field
2) The coil is on a spindle and the forces act one up and doen, it rotates.
3) Split-ring commutators swaps the contacts every half turn to keep the motor rotating in the same direction
3) The direction of the motor can be reversed either by swapping the polarity of the dc supply (reverse current) or swapping the magnetic poles over (reverse field).
4) Speed of the motor can be increased by increasing the current, adding more turns to the coil or increasing the magnetic flux density
5) Use flemings left-hand rule to work out which way the coil will turn
