Magnetism Flashcards
4.7.1 Permanent and induced magnetism, magnetic forces and fields
What is meant by the ‘poles’ of a magnet?
The poles of a magnet are the places where the magnetic forces are strongest.
What happens when two magnets are brought close together?
They exert a force on each other.
Two like poles…
…repel each other.
Two ______ poles attract each other.
unlike
The attraction and repulsion between two magnetic poles is an example of what?
A non-contact force.
Which direction do magnetic field lines go?
From the north (seeking) pole of a magnet to the south (seeking) pole of a magnet.
What is a permanent magnet?
A magnet which produces its own magnetic field.
What is an induced magnet?
A material that becomes a magnet when it is placed in a magnetic field.
What does induced magnetism always cause?
A force of attraction.
What happens when an induced magnet is removed from a magnetic field?
It loses most/all of its magnetism quickly.
What is a magnetic material?
Any material or object that can be influenced by a magnetic
field, and has the potential to become a magnet.
What is a magnetic field?
The region around a magnet where a force acts on another magnet or on a magnetic material.
List the magnetic materials (at room temperature)
Iron
Steel (alloy of iron)
Cobalt
Nickel
The force between a magnet and a magnetic material is always one of …
attraction
What does the strength of a magnetic field depend on?
The distance from the magnet.
Where is a magnetic field the strongest?
At the poles of a magnet.
How do we work out the direction of a magnetic field at a particular point?
It is the same as the direction of the force that would act on another north pole placed at that point.
Give examples of magnets
Bar magnet
Horseshoe magnet
Earth
Does the Earth have a magnetic field?
Yes
Explain how the behaviour of a magnetic compass is related to evidence that the core of the Earth must be magnetic.
-A magnetic compass contains a small bar magnet
-The north pole of compass would be
attracted to the south pole of a
bar magnet
-The north pole of a compass points to the
“top” of the earth..
-So, Earth is similar to a giant bar magnet with magnetic field lines radiating from the south to the north pole. The south pole must be at the geographical north!
Describe how to plot the magnetic field pattern of a magnet using a compass.
(1-7)
-Place a bar magnet in the middle of a piece of paper and draw around it
-Mark the north and south poles
-Place a plotting compass at the north pole
-Look at the direction that the pointer is facing
-Mark the tip with a dot
-Move the compass so the tail is on this dot and draw another dot at the tip
-Repeat until back to the magnet at the south pole
Explain how you can tell if a magnetic material is a permanent or induced magnet. [2]
Bring it near both poles of a known permanent magnet.
An induced magnetic material will always be attracted by a permanent magnet but a permanent magnet can be both attracted and repelled.
Explain why unmagnetised iron is always attracted by a permanent magnet.
The permanent magnet always induces the opposite pole next to its pole, causing the unmagnetised iron to attract.
What does a plotting compass contain?
A small bar magnet.
Describe how to plot the magnetic field pattern of a magnet using a compass.
(8-10)
-Join the dots and add an arrow to show the direction of the field line
-Repeat from different starting positions around the poles to draw multiple field lines
Why is using iron filings not a good way of showing a magnetic field?
They show the shape not the pattern of the magnetic field (i.e. the loops but not the direction).
Magnetic objects become
magnetised if placed in…
If _______ from a field, they stop
acting like magnets.
Induced magnets can only be
attracted and
A magnetic field.
Removed
Only permanent or
electromagnets can repel.
Things to remember when drawing field lines?
-Field lines never cross
-The closer the field lines, the stronger the field
-Field lines start and end on poles.
-Arrows on field lines go from north to south
What is a magnetically soft material?
A material that gains and loses magnetism quickly e.g. iron.
What is a magnetically hard material?
A material that gains and loses magnetism slowly e.g. steel.
