Transcript ELECTROMAGNETISM - Montgomery College

ELECTROMAGNETISM
The marriage of electricity and
magnetism
ELECTROMAGNETISM
Different aspects of the same force:
Electromagnetic Force
HISTORY
• Luigi Galvani = Frog
leg
• Alessandro Volta =
Voltaic pile (Battery
sandwich)
• Stacked copper and zinc
together with a layer of
wet paper between
metals producing a weak
current
Invention of the battery led to the
understanding of electromagnetism and
their symbiotic relationship
• Modern batteries
• Positive carbon rod
• Surrounded by
electrolytic paste
• Housed in a negative
zinc.
Invention of the battery led to the
understanding of electromagnetism and
their symbiotic relationship
• Therefore a battery
is a source of
conversion of some
form of energy
(magnetic) into
electric current
• Battery is a source
of EMF
Hans Oersted
• Discovered the relationship between
magnetism and electric current
• A magnetic field is produced by current
running through the wire
• Any charge in motion induces a magnetic
field
“Hand” Rules
• Right Hand rule
• Thumb indicates the
direction of the
current
• Fingers indicate
direction of magnetic
field lines
What if????
• We take a wire
• and form the wire into loops
• Does resistance increase?
• Does the magnetic field
increase? (see pg 91)
What if
• We place another coil
(B) of wire (solenoid)
next to the one that is
producing the
magnetic field? (A)
• Will this produce an
electric current. (see
pg 91)
• Take a look at the
solenoid marked A
and compare it to
solenoid marked B
• Which has more
coils?
• When Coil B is placed
in the magnetic field
of Coil A what will
happen?
a
b
• Where would there be
an increase in
voltage. A or B?
• If there are more coils
on the SECONDARY
SIDE or to the right of
the solenoid A, then
would there be more
voltage on the B side?
a
b
• Look on page 94 and
find the term
STEP-UP TRANSFORMER
Compare that definition
to the transformer on
the left
What type of
transformer is this?
a
b
Now look at the circuit below
Can you find the step up
transformer?
Number 8 is the primary side of the step
up transformer and numbers 9 are the
secondary side of the step up transformer
Now try and find it on page 117.
If the primary side of the step up
transformer has less coils than the
secondary side on a step up
transformer that would convert
Voltage to……….what is it that we use
to control the quality of x-rays???
Faraday Rule
• AKA: 1st law of Electromagnetism
• A magnetic field cannot be still and
produce a current. But if the magnet is
moving a current is produced.
Furthermore: Induced current by
a magnet depends on
•
•
•
•
Strength of magnetic field
Velocity of magnetic field
Angle of the conductor to the Magnetic field
# of turns in a conductor
TO PRODUCE electric current
•
•
•
•
Move a bar near a coil of wire
OR
Move coil of wire near stationary magnet
Current increases with increase in
magnetic field
SO WHAT IS MOVING IN AN X-RAY CIRCUIT
TO PRODUCE A CURRENT IN THE COILS?
• The current going through the step-up
transformers is AC…..Think about that…How
does AC move?
AC pulses!!!
• Which is movement! That its why AC must
be used in a step up transformer.
Numbers 15 and 14 are step down
transformers-why?????
Look at it closely…note the number of
coils on the primary side versus the
secondary side (see arrows)
Where does the current go from this
transformer?? What happens to the voltage?
LENZ’S LAW
• Most important thing to remember even if
you do not understand this law is the
following:
• It is the basis for self induction
• The autotransformer and choke coil in an xray circuit both run on self induction
HERE WE GO
Lenz’s Law: Induced current flows in
a direction such that it opposes the
action that induces it