Transcript Electromagnetism

Electromagnetism
Unit 10
History
Originally electricity &
magnetism were thought of
as 2 separate forces.
Key developments during the
early 19th century led to a
unified theory in which the
phenomena of electricity &
magnetism are known as
electromagnetism.
Hans Christian Ørsted
While preparing for a lecture, Ørsted, a
Danish physicist, made a surprising
observation.
Ørsted noticed that a compass needle
deflected from magnetic north when
the electric current from a battery was
switched on & off.
This demonstrated that electric current
passing through a wire produces a
magnetic field; confirming the direct
relationship between electricity &
magnetism.
Hans Christian Ørsted
However, Ørsted didn’t suggest
an explanation nor derive a
mathematical expression to
describe his observations.
Despite this, Ørsted published his
findings, and is credited with
proving that electric current
produces a magnetic field.
André-Marie Ampère
French physicist, Ampère was
influenced by Ørsted’s work
and through his own research,
he developed a mathematical
formula to describe the
relationship between
magnetic forces & electrical
current.
The SI unit for current (amps)
were named after him.
Michael Faraday
Although Faraday, an English
physicist, received little formal
education, he was one of the most
influential scientists in history.
Historians refer to him as having
been the best experimentalist in the
history of science.
Michael Faraday
It was Faraday’s research on
magnetic fields around a conducting
wire that led him to establish the
basis for the concept of the
electromagnetic field.
Faraday also discovered the
concept of electromagnetic
induction.
The SI unit for capacitance (farads)
are named after him.
Electromagnetic Induction
An electric current produces a
magnetic field, and vice versa,
a changing magnetic field
produces an electric current!
This motion is said to induce an
electric current (EMF) through
the coil of wire.
Moving a magnet through a
coil of wire (solenoid)produces
an electric current
Electromagnetic Induction
Solenoid
A solenoid is simply a coil of
wire.
The solenoid is the basis for
the electromagnet.
Electromagnets
Electromagnet is a magnet in
which the magnetic field is
produced by the flow of
electric charge.
Wrapping the wire around a
metal core concentrates or
increases the magnetic field
due to the additive effect of
each turn of wire.
Electromagnets
Faraday’s Law of Induction
•
ANY change in a magnetic environment of a coil of
wire will induce a flow of charge (EMF) in the coil.
∆B – change
in magnetic
field strength
Moving a
magnet toward
or away from
coil
Moving coil
into or out of B
Rotating coil
relative to the
magnet
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html
Faraday’s Law of Induction
EMF - electromagnetic field
N represents the number of loops in the wire
ΔΦB is the change in magnetic flux
Lenz’s Law
•
When an electric current is generated by a change in
magnetic flux according to Faraday’s Law, the
induced magnetic field opposes the motion of the
magnet.
Lenz’s Law
The (-) indicates that the induced magnetic field
(EMF) is always opposite the change in magnetic
flux (ΔΦB)
In other words, the magnetic field points in the
opposite direction of the change in magnetic flux.
Lenz’s Law
What is the direction of the magnetic field produced by
the induced current?
(a) ?
down
(b) ?
up
Lenz’s Law
The induced magnetic
field repels the
approaching magnet
The induced magnetic
field attracts the
departing magnet
James Clerk Maxwell
Maxwell, a Scottish theoretical
physicist, expanded upon
Faraday’s research to unify
electricity & magnetism.
Maxwell’s most prominent
achievement is the complete &
comprehensive theory which
unifies electricity, magnetism, &
light.
Maxwell’s Equations
In a set of 4 elegant equations, Maxwell demonstrated
that electricity, magnetism, & light are all a product of the
electromagnetic field!
James Clerk Maxwell
In addition, Maxwell demonstrated that magnetic &
electrical fields are self-reinforcing and travel at the
speed of light (c).
James Clerk Maxwell
Thus, he concluded that light energy travels in the form
of opposite but supporting electrical & magnetic fields in
the form of self-propagating electromagnetic waves!
James Clerk Maxwell
Maxwell’s achievements in
electromagnetism is considered
the greatest unification in
physics since Newton’s Laws!
Electromagnetic Radiation
Electromagnetic radiation, also known as light, is
energy that is propagated (moving) through space in
the form of EM waves such as radio waves, visible
light, & gamma rays.
The wavelength of light determines its energy &
characteristics.
Electromagnetic Spectrum
Electric Motor
•
•
An electric motor is an
electric machine that
converts electrical
energy
mechanical
energy.
They operate through
the interaction between
a magnetic field and
winding electric currents
to generate force.
Electric Motor
•
•
Inside the electric
motor the attracting and
repelling forces of
magnets create
rotational motion.
electrical energy
mechanical energy.
Therefore using a
electromagnetic fields to
generate mechanical
http://www.youtube.com/watch?v=MnQXnEiIUI8
motion!
Electric Generator
•
•
•
An electric generator is a
device that converts mechanical
energy
electrical energy.
Mechanical energy is used to
force electric current to flow
through an external circuit.
A magnet is moved near a wire
to create a steady flow of
charge.
Mechanical energy
electrical energy.
Electric Transformers
•
An electric transformer is a device that changes the
voltage of incoming electricity to meet the needs of
specific electric devices.
High voltage
Low voltage
- OR Low voltage
High voltage
Anatomy of a Transformer
Voltage to Coil Ratios
Primary voltage
Secondary voltage
Primary coil turns
Secondary coil turns
The ratio of the voltage to the # of coil turns
in the primary coil (input side) is equal to the
ratio in the secondary coil (output side)
1° Voltage
1° Turns
2° Voltage
2° Turns
Step-down Transformer
•
Step-down transformers are designed to reduce
voltage.
1° Coil Turns > 2° Coil Turns
Output:
Low voltage
High current.
Input:
High voltage
Low current.
Input Power
Output Power
Step-up Transformer
•
Step-up transformers are designed to increase
voltage.
1° Coil Turns < 2° Coil Turns
Output:
High voltage
Low current.
Input:
Low voltage
High current.
Input Power
Output Power
Nanoscale Motors
•
•
•
How to Cite a Website in MLA
Structure: Last name, First name. "Article Title." Website
Title. Publisher of Website, Day Month Year article was
published. Web. Day Month Year article was accessed.
<URL>.
Example:
Cain, Kevin. "The Negative Effects of Facebook on
Communication." Social Media Today RSS N.p., 29 June
2012. Web. 02 Jan. 2013.
Links
http://abyss.uoregon.edu/~js/21st_century_science/lectures/lec04.html
How to make a motor
http://www.education.com/science-fair/article/no-frills-motor/
http://www.pbslearningmedia.org/resource/psu06-nano.sci.text.lpmotorms/turning-electricityand-magnetism-into-mechanical-work-with-a-simple-motor-ms/
Animations
http://www.animations.physics.unsw.edu.au/jw/electricmotors.html