Electromagnetism Flashcards
what is a magnetic field
area around a magnet where a magnetic material will experience a force
where is the field strongest around a bar magnet
The poles - the field lines are the closest together. As you get further away, the fields get weaker.
what do magnetic field lines show
show the direction of the force that would be exerted on another north pole placed at that point - north to south on a field diagram
what happens when two magnets are brought close to each other
- they exert a force on each other
- two unlike poles attract
- similar poles repel
- examples of non-contact force
difference between permanent and induced magnet
A permanent magnet produces its own magnetic field whereas an induced magnet becomes a magnet when it is placed in a magnetic field. Induced magnets can only repel and quickly lose magnetism after being removed from magnetic field.
how does a compass show Earth has a magnetic field
- compasses contain a small bar magnet
- Earth has a magnetic field so compass points in direction of Earth’s magnetic field
how could you SHOW magnetic fields around bar magnet
- place magnet on sheet of paper
- sprinkle iron filings onto sheet around magnet
- filings will line up with the field
how could you PLOT magnet field around bar magnet
- place bar magnet on sheet of paper
- place plotting compass on paper and mark points and end of needle
- move compass to one of the points and repeat until you have a loop connecting the poles
- join lines with ruler
- repeat a different distances from the bar magnet until you have a field diagram
how is a magnetic field produced around a wire
when current flows through a conducting wire, a circular magnetic field is produced around the wire
how do you remember direction of field lines around a current carrying wire
RIGHT HAND corkscrew rule
what does strength of magnetic field around a wire depend on
the distance from the wire - the field gets weaker as you increase distance
how to make field around a wire stronger
shaping wire into a solenoid (coil) and increasing current
describe magnetic field of a solenoid
inside a solenoid it is strong and uniform with a similar shape to that of a bar magnet
how can magnetic field of solenoid be strengthened
increasing current and adding an iron core, making it an electromagnet
describe the motor effect
a conductor carrying a current is placed in an magnetic field and the magnet producing the field and the conductor exert a force on each other
describe Fleming’s left hand rule
thumb - force
index - direct of magnetic field lines
middle finger - direction of current
how can you increases size of force on a motor
- increase the current in a wire
- increase magnetic field strength
- increase number of turns on the coil to increase the length of wire within the field
how does a motor rotate
- a coil of wire carries a current in two opposite directions
- one side of a coil experiences a force in one direction, the other in the opposite direction
- with an axle through the middle, the coil will rotate
how are electromagnets used in scrapyard cranes
Steel frames of cars are attracted to the electromagnet when a current passes through the coil as it generates a magnetic field. When the current is switched off, the vehicle falls off.
how are electromagnets used in circuit breakers
- switch is held closed by a spring
- if current gets too great, magnetic field strength will increase enough to pull the switch open, and the flow of current stops
how are electromagnets used in electric bells
- current flows and armature is attracted to the electromagnet, and so the bell rings as the hammer hits the bell
- because the armature is attracted, it also opens the switch so current stops flowing in the circuit
- the armature then springs back to its original position, closing the circuit so the cycle can repeat
how are electromagnets used in relays
- relay is an electric switch
- small current magnetises the coil which attracts the armature
- this then closes the switch gap, and connects the circuit
how do loudspeakers and headphones work
Loudspeakers and headphones use the motor effect to convert variations in current from electrical circuits to pressure variations in sound waves. The varying current provides different forces to make a diaphragm oscillate, vibrating the air which produces sound.
what is the generator effect
- an electrical conductor moves relative to magnetic field and cuts through the field lines
- a potential difference is induced across ends of conductor
- if the conductor is part of a complete circuit, a current is induced
This can also be done if there is a change in magnetic field around the conductor.
