Magnetism & Electromagnetic Induction. What causes magnetism? Electrons in motion create a magnetic...
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Transcript of Magnetism & Electromagnetic Induction. What causes magnetism? Electrons in motion create a magnetic...
![Page 1: Magnetism & Electromagnetic Induction. What causes magnetism? Electrons in motion create a magnetic field. Electrons move in current, and also within.](https://reader036.fdocuments.in/reader036/viewer/2022070408/56649e565503460f94b4de7c/html5/thumbnails/1.jpg)
Magnetism & Electromagnetic Induction
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What causes magnetism?
• Electrons in motion create a magnetic field.
• Electrons move in current, and also within individual atoms
• ALL magnetism comes originally from the movement of charged particles.
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Magnets• Magnets have “polarity”
– Always two poles: north and south – Comes from magnetic domains– Like poles repel and unlike poles attract.
• There are two types of magnets:– Permanent magnets – domains are always
aligned – Temporary magnets – formed when iron-
bearing metals are brought near a magnetic field and their domains temporarily align
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The Magnet Man… Nikola Tesla
• Inventor and electrical engineer
• Widely famous for his work on AC circuits
• Pioneered wireless energy transfer to power electrical devices as early as 1873
• His unfinished “Wardenclyffe Tower” Project was meant to supply industrial power wirelessly on an international basis
• Fought with Edison for years, over AC vs. DC
• Tesla vs. Edison
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Magnetic FieldsMatch the diagrams with the magnetic fields below.
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Magnetic field - the space around a magnet over which the magnetic force exists
• The more field lines, the stronger the magnetic field• Field lines ALWAYS point from north to south• Magnetic Field strength is measured in Teslas (T)
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Direction of Magnetic Field
• The direction is the same as where the north pole of a compass points when it is placed in the magnetic field.
• So, field lines come out of the magnet at its north pole and enters at its south pole.
• Magnetic field lines are most concentrated at the poles (the field is stronger at the poles)
• Remember… opposites attract, likes repel!
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Draw the magnetic field lines below.
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Draw the magnetic field lines below.
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Electromagnets
• Electromagnets – devices that use electric current to produce a concentrated magnetic field
• Iron in a coil of current carrying wire will become an electromagnet.
• Temporary magnets• Some uses: telephone relays,
levitation, magnetic cranes,
sorting metal, MRI
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Electromagnetism• Christian Oersted discovered that electric current in
a wire creates a magnetic field.
• Current, moving in a straight
wire, produces a magnetic
field surrounding the wire.– We can see this with a compass...
• But, since the field goes around the wire, how do we know which way it goes?
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The Right Hand Rules (RHR)
• Rules to help you determine magnetic field direction, using your RIGHT hand.
• First RHR – current in a straight wire– Grasp the wire with your right hand. – Thumb is in the direction of the positive current.
– Fingers circle the wire and point in the direction
of the magnetic field (circular).
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We Use Two RHRs:(there are actually three)
• First RHR: current in a straight wire– Grasp the wire with your right hand. – Point thumb in the direction of the current – Fingers circle the wire and point in the direction of the
magnetic field (circular)
• Second RHR: current in a coiled wire– Grasp the coil with your right hand. – Curl fingers around the loops of wire in the direction of the
current – Thumb points toward the NORTH pole of the electromagnet
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1st RHR
Note: current traveling in opposite directions in a wire, will have magnetic fields in opposite directions
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2nd RHR
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More on Electromagnetism• Loops of wire produce stronger
electromagnets than straight wire
• The more loops of wire, the stronger the field
• Thicker wire produces a stronger magnet
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Using the RHRs • Use right hand rules to draw the magnetic field
lines.– The “dot” means current is coming out of the page– The “x” means current is going into the page
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Electromagnetic Induction• Faraday’s Discovery:
– Faraday found he could induce current by moving a wire in a magnetic field.
• If the wire moves up through the field the current moves in one direction.
• If the wire moves down through the field the current moves in the opposite direction.
• If the wire moves parallel to the field lines no current is produced.
• Electromagnetic Induction: the process of inducing current in a wire due to the relative motion of the wire and/or the magnetic field
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Electromagnetic Induction
Observing Faraday’s Experiment:
Faraday’s Experiment 1
Faraday’s Experiement 2
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Electric GeneratorsConvert mechanical energy to electrical energy
• How it works:– Mechanical energy turns an armature
• armature: wire wrapped around an iron core in a magnetic field
– The induced voltage causes current to flow.
• A generator at work
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Electric Generator
• The strength & direction of induced current changes as the armature rotates
• Induced current is maximum when the wire loops move through the strongest areas of the magnetic field
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Alternating Current (AC) Generators
• The direction of the current switches back and forth at some frequency
• The faster the coil turns, the faster the directions changes, so the higher the frequency.
• Let’s Look
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Is it AC or DC?
• Wall plugs provide AC, batteries provide DC
• Electricity transmission systems (grids) are AC, but operate on different frequencies – Five in the U.S. alone– Why you can’t plug your stuff directly into the wall
in Europe
• High-Voltage DC can connect AC systems running on different frequencies
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Motor vs. Generator• What’s the difference?
– Motor: Electrical to Mechanical Energy– Generator: Mechanical to Electrical Energy
• Can sometimes be used interchangeably, like in a vehicle– Motor when accelerating – battery provides
energy to run motor– Generator when braking – inertia used to
recharge battery
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Transformers
• Used to change AC voltage
• Very efficient (little energy lost to heat)
• How they work:– two coupled coils are attached using a metal
bar (usually a ring or “U”)– the coils have different numbers of loops
• One is the primary coil • The other is the secondary coil
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Types of Transformers:Step-Up or Step-Down
• Step-Up:– More turns (loops) in the SECONDARY coil– The secondary voltage is greater than the primary
voltage
• Step-Down:– More turns (loops) in the PRIMARY coil– The primary voltage is greater than the secondary
voltage