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## Electromagnetic Induction

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Title: Electromagnetic Induction

1
Electromagnetic Induction
• Physics
• Dr.E

2
• Electromagnetic Induction
• Motors/Generators http//science.howstuffworks.com
/motor4.htm
• Transformers
• Power Transmission
• Solenoids
• MRI

3
The Magnetic Field
• The electric field proves a useful concept to
explain the effects of charge at a distance
(explains how one charge knows another charge is
there).
• Stationary charges produce only an electric field
• Moving charges (in flux) produce both an electric
field and a magnetic field

4
• Electromagnetic Induction
• Motors/Generators http//science.howstuffworks.com
/motor4.htm
• Transformers
• Power Transmission
• Solenoids
• MRI

5
Motors
• Motors work due to two major principles
• Opposite poles attract while like poles repel
• Current running through a coiled wire creates a
magnet

6
Theory
7
Mechanics
8
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9
• Electromagnetic Induction
• Motors/Generators http//science.howstuffworks.com
/motor4.htm
• Transformers
• Power Transmission
• Solenoids
• MRI

10
• The voltage induced in a coil is proportional to
the number of coils times the magnetic flux (rate
at which the magnetic field changes)

11
Wrap Rule to find Magnetic Field
1. Wrap your fingers in the direction of the current
2. The magnetic field points in the direction of the
thumb (to the left)
3. Since the field lines leave the left end of
solenoid, the left end is the North pole

12
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• An ammeter is connected in a circuit of a
conducting loop
• When a bar magnet is moved closer to, or farther
from, the loop, an electromotive force (emf) is
induced the loop
• The ammeter indicates currents in different
directions depending on the relative motion of
magnet and loop
• When the magnet stops moving, the current returns
to zero as indicated by the ammeter

14
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15
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16
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17
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18
• Electromagnetic Induction
• Motors/Generators http//science.howstuffworks.com
/motor4.htm
• Transformers
• Power Transmission
• Solenoids
• MRI

19
Primary Voltage of 1o turns
Secondary Voltage of 2o turns
20
(Power IN)
(Power OUT)
21
(Voltage x Current)secondary
(Voltage x Current)primary
22
• Electromagnetic Induction
• Motors/Generators http//science.howstuffworks.com
/motor4.htm
• Transformers
• Power Transmission
• Solenoids
• MRI

23
Power Transmission
• Plant
• 6000 V and 20Amps
• Local and Homes
• 120 V and 100 Amps
• Low Voltage Wires
• 2200 V and 54 Amps
• High Voltage Wires in Town
• 120,000 V and 1 Amp
• Ultra High Voltage
• 400,000 V and 0.3 Amps

24
• Electromagnetic Induction
• Motors/Generators http//science.howstuffworks.com
/motor4.htm
• Transformers
• Power Transmission
• Solenoids
• MRI

25
Solenoids
• The magnetic field of a solenoid is essentially
identical to that of a bar magnet.

The big difference is that we can turn the
solenoid on and off ! It attracts/repels other
permanent magnets it attracts ferromagnets, etc.
26
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27
Solenoid Applications
• Digital on/off
• Doorbells
• Power door locks
• Magnetic cranes
• Electronic Switch relay
• A small current can be used to switch a much
larger one
• Starter in washer/dryer, car ignition,

28
Solenoid Applications
• Analog (deflection a I )
• Variable A/C valves
• Speakers

Solenoids are everywhere!
29
• Electromagnetic Induction
• Motors/Generators http//science.howstuffworks.com
/motor4.htm
• Transformers
• Power Transmission
• Solenoids
• MRI

30
Thanks to
31
MRI / NMR
If we bathe the protons in radio waves at a
particular frequency, the protons can flip back
and forth. If we detect this flipping ?
hydrogen! The presence of other molecules can
partially shield the applied magnetic field, thus
changing the resonant frequency (chemical
shift). Looking at what the resonant frequency
is ? what molecules are nearby. If a strong
magnetic field gradient is produced across the
sample, can look at individual slices, with
millimeter spatial resolution.
32
Bibliography
• Magnetism Examples of Magnetic Field