Download Magnetism Magnetic Force What causes magnetism?

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Magnetism
Top view of iron filings sprinkled around a
magnet. The filings trace out a pattern of
magnetic field lines in the space surrounding the
magnet. Interestingly, the magnetic field lines
continue inside the magnet (not revealed by the
filings) and form closed loops.
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Magnetic Force
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What causes magnetism?
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Magnetism
Magnetism
The 1st Right Hand Rule
II. Electric currents produce magnetism
Hans Christian Oersted, in 1820, accidentally discovered that
a compass needle was affected by a nearby electric current.
The electric current produced a magnetic field.
Magnetic fields are caused by moving electric charges.
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When to use: To find the
direction of the magnetic field
around a current carrying
wire.
How to apply: Point your
thumb in the direction of the
positive charge flow
(conventional current). Your
fingers wrap to show the
direction of the magnetic
field.
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Earth is a Magnet
• A suspended magnet or compass points northward
because the Earth itself is a huge magnet. The
compass aligns with the magnetic field of the Earth.
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What Causes Magnetism?
• Electric Current Causes Magnetism
In 1820 a Danish HS teacher (Hans Orsted) made amazing
discovery. Wire carrying current deflects a magnet. Basis of
telegraph, radio, TV
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Magnetic Force on Current
carrying wire
Solenoids: Electromagnets
Appropriate materials can be mad into
magnets and this magnetic filed can be
turned on and off, e.g. videotape
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Charges and magnetic Fields
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Magnetic Force on CurrentCarrying Wires
• A charged particle at rest
will not interact with a
static magnetic field. But if
the charged particle is
moving in a magnetic
field, the magnetic
character of a charge in
motion becomes evident.
It experiences a deflecting
force
• Simple logic tells you
that if a charged
particle moving through
a magnetic field
experiences a
deflecting force, then a
current of charged
particles moving
through a magnetic
field experiences a
deflecting force also
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When the current flows in the
wire that is placed in the
magnetic field as shown, the
wire is forced upward. If the
wire is made to form a loop as
shown, the loop will tend to
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When the current flows in the
wire that is placed in the
magnetic field as shown, the
wire is forced upward. If the
wire is made to form a loop as
shown, the loop will tend to
1. rotate clockwise.
2. rotate counterclockwise.
3. remain at rest.
1. rotate clockwise.
2. rotate counterclockwise.
3. remain at rest.
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Can this property be
harnessed?
The Speaker
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Meter
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Electromagnetic Induction
•If a wire carrying current causes a magnetic
field, is the inverse thru i. e. does a magnetic
field cause current?
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Lenz’s Law
• If a wire carrying current causes a
magnetic field, is the inverse thru i. e.
does a magnetic field cause current?
An induced current flows in such a direction so that the
magnetic field it creates opposes the change in magnetic
flux that causes the current.
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Faraday’s Law
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Faraday’s law
•The induced
voltage in a coil
is proportional to
the product of
the number of
loops and the
rate at which the
magnetic field
changes within
those loops.
Energy In EM Field
Summary of EM Induction
• Move a magnet near a electrical conductor and
current flows in the conductor
• Move conductor near a stationary magnet and
current flows in conductor
• Make an Electromagnet by passing current thru it,
move it near conductor and current flows in 2nd
conductor (loop)
• Place 2 conductors in proximity, change the current
in one conductor, current flows in other conductor
A changing magnetic field produces an
electric field
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Generators and AC Current
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Transformer: A device used to
increase or decrease an alternating
potential difference.
Transformers
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• We see that if the secondary has more
voltage than the primary, it will have
less current than is in the primary. The
ease with which voltages can be
stepped up or down with a transformer
is the principal reason that most electric
power is ac rather than dc.
• Check yourself
• 1. If 100 V of ac are put across a 100-turn
transformer primary, what will be the voltage
output if the secondary has 200 turns?
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Power Transmission
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Electron in magnetic Filed
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Charged particle In magnetic
and electric fields
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