# Lesson-4---Magnetism 3

```Magnetism
Book page 179 – 182
03/10/2020
Syllabus 6.2 – 6.10
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How does magnetism work?
Saturday, 03
October 2020
Keywords: friction, stopping distance, momentum, crumple zone
DO NOW: QUIZ FOR 5!
1. What is the formula for force?
F=MxA
2. What is the resultant force of the pictures on the
right?
30N, 20N, 0N
3. What are the two forces responsible for terminal
velocity
Gravity and air resistance
4. What is the unit for force?
Newtons
5. What is the acceleration of an object with a mass
of 3Kg that is been acted on by a force of 300N?
A=F/M 300/3= 100m/s2
How does a maglev train
work?
Starter
• Have you ever
wondered…..
• ….how does a Maglev
Train work?
• How Maglev Trains Work
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Aim
- Explain how you can test for a magnet
- Describe the shape and direction of a magnetic field around a current
carrying wire and around a solenoid
Key Words
• Hard magnet
• Soft magnet
• Domain
• Right hand rule RHR 1 and 2
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Learning Objective
• Describe the properties of magnetically hard and soft materials.
• Understand the term ‘magnetic field line’ and magnetism can be
induced
• Know that magnetism is induced in some materials when they are
placed in a magnetic field.
• practical: investigate the magnetic field pattern for a permanent bar
magnet and that between two bar magnets
• Describe how to use two permanent magnets to produce a uniform
magnetic field pattern.
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How do animals use magnetic fields?
The big picture
Have you ever wondered
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Think-Pair-Share
• Why are magnets able to attract objects?
• How does gravity pull every objects to the
earth?
End
What do you think we call the space around an object
where it can affect other objects.
FORCE FIELDS
What is a
magnetic field?
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Magnetic fields
• Magnetic field is a region in which
a magnetic force can be detected.
• Magnetic field lines can be drawn
with the aid of a plotting compass.
• The compass will point in the
direction of the field, NOT the
north pole
• A normal compass points in the
direction of the N-pole
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Another method
• You can see the shape of the magnetic field
around a magnet by using iron fillings
• Strong magnetic field lines are close
together
• Magnetic field lines never cross
• Magnetic field lines are symmetric
• Magnetic field lines point from N to S
outside the magnet but inside the magnet
they go from S to N
Different magnetic fields
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What is a magnet?
Discuss the question in your groups for 1 minute.
Un-magnetised piece of metal
S
N
Magnetised metal
S
N
• Magnetic material: iron, nickel, cobalt
• Magnets are able to attract these materials
• A magnet has a north and a south pole  mono poles have
• Equal poles repel, opposite poles attract
• Permanent magnets are hard to magnetize but they stay
magnetized
for a long time. They are called hard magnets  made from steel
• Temporary magnets are easy to magnetize, but they easily lose
their magnetic properties. They are called soft magnets  made
from iron
• Magnetism can be induced in a magnetic material by leaving it in
a magnetic field
Magnets repel and attract
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What happens?
S
N
S
N
S
S
N
N
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N
hold
up their
How can Everyone
you make acollect
magnetand
using
electricity?
Saturday, 03
green October
pen 2020
What is potential difference?
The work done per unit charge in a circuit
How do we measure potential difference?
In parallel
What is resistance?
The opposition to the flow of current
Which formula connects resistance,
current and voltage? V=I X R
Calculate the potential difference(voltage)
across an bulb if its resistance is 3 ohms Do next: How do we
and the current is 13A?
make magnets using
electricity?
V=IxR = 3x13 = 36V
How can you test for a magnet?
• The only true test for a magnet is repulsion.
Since S and R both attracted to
Q, the rod is only made of
magnetic material, but is not a
magnet
Only U repels Q, therefore only
rod 3 is a magnet
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How does a magnet become a magnet?
• Inside magnetic metals are group of atoms, domains, which act like tiny magnets
Domains
• The iron on the left is un-magnetized.
• You can magnetize these materials by stroking them in one direction with a magnet, this is to line up
the domains
• Methods of de-magnetizing: you need to scramble the domains by:
- Hammer it
- Heat it
- Wrap a coil around it and pass an alternating current through it
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Recap magnet
Self Assessment
Cutting a bar magnet in half
Describe :If a bar magnet is cut in half, if it will produces
two smaller bar magnets.
Explain: The domains are still aligned within the two new
bars. The split means the left magnet has a north and
south pole as does the magnet on the right.
S
N
S
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N
An iron or steel bar which has not been magnetised.
N
No magnetic
force field
S
S
N
Atomic Magnets all jumbled pointing at each other: Their fields cancel each other and
this iron or steel bar would not be magnetic
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What is electromagnetism?
Saturday, 03
October 2020
Quiz for 5
1. What is velocity?
How fast you are going in a particular direction
2. What is a scalar quantity?
A quantity with magnitude and no direction
3. Which graph is used to calculate
acceleration?
Velocity –time graph
4. What is the distance travelled by a ball
fired from a cannon at 10m/s upwards
if if acceleration due to gravity is
10m/s2? Hint use V2=U2 +2as S= V2-U2 /2a = -100m/s/20 =50m
5. What was the total distance travelled by
50m x 2 =100m
the ball?
Unmagentized steel or iron bar
S
N
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The magnetic force field from the permanent magnets
line up the atomic magnets and will make the steel or
iron bar magnetic.
S
N
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The magnetic force field from the permanent magnets
lines up the atomic magnets and will make the steel or
iron bar magnetic.
S
N
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The magnetic force field from the permanent magnets
lines up the atomic magnets and will make the steel or
iron bar magnetic.
S
N
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The magnetic force field from the permanent magnets
lines up the atomic magnets and will make the steel or
iron bar magnetic.
S
N
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The magnetic force field from the permanent magnets lines up the
atomic magnets and will make the steel or iron bar magnetic.
N S
N
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S
The blue magnet now has its own magnetic field
N
S
E J Vine.
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TEMPORARY MAGNETS ARE MADE OF IRON :
When the domains are lined up the bar becomes magnetic.
The domains in pure iron are easily lined up, iron is easy to magnetise.
N
S
S
N
However, even the warmth of the room gives the domains
enough energy
to jumble up again and the bar easily looses its magnetic
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2015
field.
Heat from the room is sufficient to give the domains energy, this
destroys the orderly lines, the magnetic field will disappear.
S
N
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The magnetic force field gradually disappears.
N
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No field left!!!!
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Permanent MAGNETS ARE MADE OF Steel plus impurity atoms like Al aluminium, Ni nickel, Co cobalt
N
S
S
N
Al
Ni
Co
The impurity atoms make it difficult to magnetise Al Ni Co magnets but they also lock the domains in position once
they are lined up.
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Permanent MAGNETS ARE MADE OF Steel plus impurity atoms are heated
N
S
S
N
Al
Ni
Co
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What is Electromagnetism
When a current flows through a wire a magnetic field is created
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Electromagnets
A wire with an electric
current flowing through it has
………………
magnetic field around it.
a …………………
wire
When the ………… is wrapped
field
into a coil, the magnetic …………
is a similar shape to the
magnetic field of a bar
magnet .
………………
KEYWORDS:
Wire
Magnet
Current
Field
Magnetic
EXTENDING: Suggest a
difference between an
electromagnet and a
bar magnet.
Investigating Electromagnets
Draw a circuit diagram for an electromagnet.
Include a switch in your diagram.
Challenge: can you remember the 3 things that
affect the strength of a magnet?
Demonstration
The object on the left is an
electromagnet. The object on
the right shows how an
the lab.
How is a
magnetic field
created using
this device. .
With an
electric
current.
How can you measure the strength of the electromagnet?
Making and testing a electromagnet.
• Wrap the wire around the
iron nail.
• Connect a crocodile clip to
each end of the wire
• Plug the other end of the
wires into the Power pack.
• Turn the Power Pack on.
Challenge: What could you do to increase the
number of coils?
Magnetic
Field of a
Current
• Solenoids produce
Loop
a strong magnetic
field by combining
several loops.
• A solenoid is a long,
helically wound coil
of insulated wire.
Increasing
strength
• The strength of the field around a
solenoid can be increased by
• Increasing the current through the
solenoid
• Increasing the number of turns of the
solenoid
• Wrapping the solenoid around
magnetically soft core such as iron
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Exam question (Foundation)
List the ways an electromagnet can be made
stronger.
(key words: paper clips, magnet, number of turns)
Challenge Exam question. (Higher)
Describe how you would construct a
electromagnet and explain how increasing the
number of coils can increase the strength of the
magnet.
(key words: paper clips, magnet, wire, crocodile
clips; electric field)
Challenge Exam question. (Higher)
Exam question
(Foundation)
• More coils.
• More current.
• Larger area
(thicker coil).
• Bigger magnet.
• Wrap the wire around the
iron nail.
• Connect a crocodile clip to
each end of the wire.
• Plug the other end of the
wires into the Power pack.
• Turn the Power Pack on.
Explaining
• More turns.
• More current.
• Stronger field strength