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Magnetism
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Laws of Magnetism
Magnetic fields
Magnetic Materials
Magnetic Properties of Matter
Forces Between Magnets
Magnetic Effects of a Current
Induced Magnetism
Methods of Magnetism
Theory of magnetism
&
Demagnetization
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Done By: Siddharth Arora
Laws of magnetism
Like poles _________
Unlike poles _______
1) repel; attract
2) attract; repel
3) explode; melt
4) disintegrate;
fly to the moon
Question 3
Question 2
Question 1
Instructions:
Click on the correct answer
Laws of magnetism
Which ones of the poles are
North?
Question 3
Question 2
1) A,B
2) none
3) B,C
4) B,D
Question 1
Instructions:
Click on the correct answer
Laws of magnetism
Magnetic North is geographical
_______
Question 3
Question 2
1) South
2) East
3) Space time continuum
4) Centre of the Universe
Question 1
Instructions:
Click on the correct answer
Laws of Magnetism
• When a bar magnet is
suspended freely it always
comes to rest in a north south
direction.
Magnetic Poles
• Magnetic South is
geographical
North.
• Magnetic North is
geographical South
Magnetic Poles
• Magnetic poles are located at
the side of the magnets.
Magnetic & Non-Magnetic Materials
• Magnetic Materials include:
– Iron
– Cobalt
– Nickel
• The rest are alloys of these
metals such as steel.
Forces Between Magnets
• Like Poles Attract
• Unlike Poles Repel
Induced Magnetism
• A magnet attracts a non
magnetic material by magnetic
induction
Methods Of Magnetization
• Heating and Hammering
– Place a steel bar in the northsouth direction and heat
– Hammer it while cooling
A magnet formed by this method is __________
A) Strong
B) Weak
Try This Question
Methods Of Magnetization
• Heating and Hammering
– Place a steel bar in the northsouth direction and heat
– Hammer it while cooling
A magnet formed by this method is weak
Methods Of Magnetization
• Heating and Hammering
– Place a steel bar in the northsouth direction and heat
– Hammer it while cooling
A magnet formed by this method is weak
Methods of Magnetization
• Magnetization by stroking
– Done as shown in diagram
A magnet formed by this method is __________
A) Strong
B) Weak
Try This Question
Methods of Magnetization
• Magnetization by stroking
– Done as shown in diagram
A magnet formed by this method is weak
Methods of Magnetization
• Magnetization by stroking
– Done as shown in diagram
A magnet formed by this method is weak
Methods of Magnetization
• Magnetization using an electric current
– A solenoid (a length of copper wire wound into a long coil) is connected to a
battery in series.
– A iron bar is then placed inside the solenoid
– The polarities depend no the direction of the flow of the current
A magnet created in this way is ________
A) Strong
B) Weak
Try This Question
Methods of Magnetization
• Magnetization using an electric current
– A solenoid (a length of copper wire wound into a long coil) is connected to a
battery in series.
– A iron bar is then placed inside the solenoid
– The polarities depend no the direction of the flow of the current
A magnet created in this way is strong
Methods of Magnetization
• Magnetization using an electric current
– A solenoid (a length of copper wire wound into a long coil) is connected to a
battery in series.
– A iron bar is then placed inside the solenoid
– The polarities depend no the direction of the flow of the current
A magnet created in this way is strong
Demagnetization
• A solenoid (a length of copper wire wound into a long coil) is
connected to a battery providing alternating current.
• The magnet is then placed inside the solenoid
• It is then removed in an East-West direction
Theory of Magnetism
• Magnetic domains (groups of small atomic magnets) are found in each
magnet.
• A magnet is formed when all the domains point in one direction.
Magnetic Fields
• The region around the magnet
where its effects can be
observed is a magnetic field
Magnetic Fields
• Properties of magnetic fields
– Outside the magnet the lines
start from the north pole and end
at the south pole
– Inside the magnet they continue
from the south pole to the north
pole
Magnetic Fields
– The lines never cross each other
– The lines behave as though they
are pulled taut
– The lines repel each other
– Lines are close together in a
stronger field than a weaker field
Magnetic Fields
– The lines tend to pass through a
magnetic substance
Magnetic Properties of Matter
• Soft Magnetic Materials
–
–
–
–
Easy to magnetize
Easy to demagnetize
Can be used as electromagnets
E.g.: Iron
Magnetic Properties of Matter
• Hard Magnetic Materials
– Hard to magnetize
– Hard to demagnetize
– Can be used as permanent
magnets
– E.g.: Steel
Magnetic Properties of Matter
• Permanent magnets
– Magnetism is retained for a long
time
Magnetic Properties of Matter
• Electromagnets
– Magnetic events can only be
observed for specific intervals of
time
Magnetic Properties of Matter
• The strength of an
electromagnet can be increased
by:
– Passing a larger current through
the solenoid
– Increasing the number of turns of
the solenoid
Magnetic Properties of Matter
– Inserting a core of a soft magnetic material
A core of a hard magnetic material cannot be used
because____________
A) It takes too long to magnetize and demagnetize
B) Its not cool
Try This Question
Magnetic Properties of Matter
– Inserting a core of a soft magnetic material
A core of a hard magnetic material cannot be used
because It takes too long to magnetize and
demagnetize
Magnetic Properties of Matter
– Inserting a core of a soft magnetic material
A core of a hard magnetic material cannot be used
because It takes too long to magnetize and
demagnetize
Magnetic Effect of a Current
• Magnetic effects of current means
that a current flowing in a wire
produces a magnetic field round it.
• As current increases more lines are
formed
Magnetic Effect of a Current
• Maxwell’s Corkscrew rule states
that the direction of the
magnetic field is the same as the
direction in which you would
turn an ordinary corkscrew to
move it in the direction of the
current.
Magnetic Effect of a Current
• This can be interpreted as when
current is flowing downwards
or away from you, the magnetic
field is in the clockwise
direction
Magnetic Effect of a Current
• The magnetic field when the
wire is in the shape of a flat coil
or a solenoid, is shown in the
diagram