Chapter 9 (9.1 - 9.8) - Magnetism Flashcards
What are poles of a magnet
Points of the magnet where the magnetic force originates from
What happens to like poles
What happens to unlike poles
Like poles - repel
Unlike poles - attract
Relationship between force between poles and distance
Inversely proportional. As distance decreases, force between the poles increases.
Why are metals attracted to magnets
Induced magnetism - when a magnet is nearby, the metal itself becomes a magnet with unlike poles to the original magnet. This leads to the metal being attracted.
What is a permanent magnet
eg
Keeps some of its induced magnetism even after its pulled away from the magnet
eg steel
What is a temporary magnet
eg
Loses all its induced magnetism after it is pulled away from the magnet
eg iron
2 ways to make a magnet
which is more effective
Stroke the metal with the magnet
Put the metal in a metal coil and pass a one way current through it (dc)
Current method is more effective
What are magnetic materials (definition)
mention the 2 types
Can be magnetized and is attracted to magnets
2 types:
hard
soft
What are ferromagnetics
Strongly magnetic materials
Explain what hard magnetic materials are
eg and use case(s)
Materials that are difficult to magnetize but do not readily lose their magnetism
eg: steel, alcomax
use: permanent magnets
Explain what soft magnetic materials are
eg and use case(s)
Materials that are relatively easy to magnetize but their magneitsm is temporary
eg: iron, mumetal
use: electromagnets and transformers
How to demagnetize a mateiral
Hammer it repeatedly
heat it to a high temp
Pull out of a coil with AC current flowing thru it
What is the magnetic field
Region around the magnet that exerts a force on the magnetic materials in it
What is the neutral point
Point between 2 like poles where the field lines exactly cancel eachother out and the magnetic force is 0
What happens to the magnetic field lines if two poles are placed near each other
Magnetic fields combine with each other to produce a single field.
What happens when a current is passed through a wire
A weak magnetic field is produced
Properties of magnetic field when current is passed through a wire
Magnetic field lines are circled
Field lines are strongest closet to the wire
Increasing the current would increase the strength of the field
What is the rule for finding field direction when a current is passed through a wire
what shows what
Right-hand thumb rule.
Thumb points in the direction of the conventional current
Fingers point in the same direction as field lines
What is a solenoid
A long coil
Magnetic field produced in a single coil vs solenoid (properties)
Magnetic field is strong in solenoid since there are more coils
Increasing the current would increase the magnetic field produced
Same field lines as a bar magnet
Components of an electromagnet
A coil (usually copper)
A core (usually iron)
Why does an electro magnet work
When current is passed through a coil, a weak magnetic field is generated. This magnetisezes the core (induced) which creates a much more powerful magnetic field than jus the coil alone
How to increase strength of magnetic field
Increasing current
Increasing number turns in coil
Why is a force generated when a current is passed through a wire which is in an electric field
what rule is used to find the direction of the force
acronym
The current produces its own magnetic field which acts upon the poles of the magnet, generating a force.
Fleming’s Left hand rule
FBI (force, direction of magnetic field, direction of current)
What happens to a beam of charged particles (eg electrons) as they pass a magnetic field
A force acts upon them
eg current
When does flemings left hand rule not work
When the current and field are in the same direction, there is no force thus the rule doesnt work
What is the turning effect on a coil
When a rectangular coil is in between a magnetic field and a current is passed through it a turning effect is generated. This is because the current travels in opposite directions at either end of the coil, pushing one side up and one side down
How to increase the turning effect on a coil
Increase the number of turns in the coil
Components of a DC motor
Battery
Brushes
Split ring
Coil
Magnet
What does a split ring do
aka
Changes the direction of the current so that the force changes direction and the coil continues to rotate
Commutator
When does the coil have maximum turning effect (DC motor)
When it is horizontal
How to increase the turning effect of coil in DC motor
Increase area of coil
Stronger current
More number of turns in the coil
Stronger magnet
What is electromagnetic induction
what happens
Induction of current as wire moves across a magnetic field
an EMF is induced
What is a galvanometer
A meter that is sensitive to very small currents.
How to increase induced EMF
Move wire faster
Use a stronger magnet
increase length of wire in the magnetic field (eg: looping the wire)
What is Faraday’s law
The emf induced in a conductor is proportional to the rate at which magnetic field lines are cut by the conductor
How to reverse the direction of the induced emf
Move the wire in the opposite direction
Turn the magnet around so that the field direction is reversed
When is there no induced emf
When the wire is not moving
When the wire is moving parallel to the magnet field lines (not cutting)
Why is there an induced EMF when a bar magnet is pushed into a coil
Magnetic field lines are still being cut by the wire as the bar magnet moves in and out of the coil.
How to increase the induced EMF of a magnet being pushed into a coil
Move the magnet faster
Use a stronger magnet
Increase number of turns in the coil (increases the length of the wire cutting through the magnetic field)
When is the direction of induced emf (and current) reversed between a bar magnet and a coil
When the magnet is pulled out
When the south pole is pushed in instead of the north
When is there no induced EMF between a magnet and the coil
When the magnet is held still (no field lines are being cut)
What is lenz’s law
Induced current always flows in a direction such that it opposes the change that produced it
What does fleming’s right hand rule find
what shows what
Direction of induced current
thumb - motion
index - field
middle finger - induced current
When does fleming’s left hand rule apply
when does fleming’s right hand rule apply
Left: When current causes motion
Right: When motion causes current
which component is the ac generator connected to
primary coil
what are brushes used for
prevents friction, prevents loss of current
Where are split rings used
where are slip rings used
slip - generator
split - dc motor
how do electrons move
negative to positive
how does current move
positive to negative
how do compasses tilt
align with magnetic field lines
points to south if field lines move from N to S
