Download Electromagnetism - David Brotherton CCCMC

Unit 6 Electromagnetism
Class Notes
Phy.3.2.2 Explain how electric currents produce various magnetic fields.
Phy.3.2.3 Explain how transformers and power distributions are applications of electromagnetism.
Extension – Induced emf and magnetic flux
-Faraday’s Law of Induction
-Large Motional Emf of objects in orbit
Electromagnetism: An electric current flowing through a wire
that gives rise to a magnetic field. See Page 568 of Conceptual
Physics.
 The direction of the magnetic field depends on the direction
of the current.
 Fleming’s Right-hand Rule
 When a wire that is carrying current is wrapped, coiled or
twisted, the magnetic fields produced by each loop are added
together.
Solenoid: A long coil of wire with many loops that produce
magnetic fields.
The power can be increased by adding more coils and
decreased by removing coils.
Electromagnet: A solenoid with a magnetic material such as iron
(Fe) inside the coil.
Electromagnetic Induction: The process by which a current is
produced by a changing magnetic field.
Discovered by Michael Faraday (English Physicist and Chemist
(1791-1867))
Faraday’s Law of Induction- The induced electromotive force in
any closed circuit is equal to the rate of change of
the magnetic flux through the circuit.
where
is the electromotive force (EMF) and ΦB is the magnetic flux.
0r, in common terms- The amount of voltage created is equal to
the change in magnetic flux divided by the change in time.
The bigger the change you have in the magnetic field, the
greater amount of voltage
Magnetic flux - Magnetic flux (most often denoted as Φm), is a
measure of the amount of magnetic field passing through a
given surface (such as a conducting coil). The SI unit of
magnetic flux is the weber (in derived units: volt-seconds).
The CGS unit is the Maxwell.
EMF – Electromagnetic Field - In the past, electrically charged
objects were thought to produce two different, unrelated
types of field associated with their charge property.
An electric field is produced when the charge is stationary
with respect to an observer measuring the properties of the
charge, and a magnetic field (as well as an electric field) is
produced when the charge moves (creating an electric
current) with respect to this observer. Over time, it was
realized that the electric and magnetic fields are better
thought of as two parts of a greater whole — the
electromagnetic field.
Galvanometer: An instrument used to detect small currents
(Amps).
Induced Current: Current created by a change in a magnetic
field.
How is this used:
Generator: A device that converts mechanical energy into
electrical energy through electromagnetic induction. Creates
AC current. Using Fadraday’s Law, a wire is spun in a
magnetic field producing a current. Anything that can spin
the turbine, can be used to produce electricity.
http://videos.howstuffworks.com/discovery/30198-really-bigthings-hydroelectric-power-video.htm
Electric motor: A device that changes electrical energy into
mechanical energy.
Transformer: A device that increases or decreases the voltage of
alternating current.
A step down transformer has fewer loops in the secondary
coil.
A step up transformer has more loops in the secondary coil.
𝑃𝑟𝑖𝑚𝑎𝑟𝑦 𝑣𝑜𝑙𝑡𝑎𝑔𝑒
𝑠𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦 𝑣𝑜𝑙𝑡𝑎𝑔𝑒
Equation: 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑟𝑖𝑚𝑎𝑟𝑦 𝑡𝑢𝑟𝑛𝑠 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑠𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦 𝑡𝑢𝑟𝑛𝑠
Remember that the power going into a transformer is the same as the power
coming out
Pin = Pout
Step Down Vsdown
Step Up
Isup
Vsup
Isdown
Step-up transformer
Step-down transformer
How they are used
For more information- text –pp.562 to 591
Or go to
http://www.michaelsharris.com/electronics/week2/transformers.ht
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