Transcript Maxwell´s Equations - The Astro Home Page

Maxwell’s Equations
- Gauss’s law, which is generalized
form of Coulomb’s law, that relates
electric fields to electric charges.
- Gauss’s law for magnetic fields, except
that there are no magnetic monopoles.
Magnetic field lines are always
continuous.
- Faraday’s law: an electric field is
produced by changing magnetic field.
- a magnetic field is produced by an
electric current, or by a changing electric
field.
Maxwell’s Fourth Equation:
Displacement Current
Maxwell resolved the problem of no
current through the capacitor by stating
that the changing electric field between
the plates is equivalent to electric
current.
Such strange current is called
displacement current.
The ordinary current is then called a
conduction current.
Production Of Electromagnetic
Waves
-the electric and magnetic fields at any
point are perpendicular to each other and
to direction of motion;
-fields alternate in direction from point to
point;
-the electric and magnetic fields are “in
phase”.
EM waves are produced by accelerating
electric charges.
Speed of EM Waves
v
1
 0 0
Electromagnetic Spectrum
Example
Calculate the wavelength:
(a)Of a 60-Hz EM wave;
(b)Of a 93.3 MHz FM radio wave;
(c)Of a beam of visible red light from a
laser at frequency 4.74x1014 Hz.
1. Which of the following a/m waves has the highest
frequency: radio, microwaves, visible light, ultraviolet
light, or X-rays?
2. What is the difference between X rays and gamma rays?
3. Which of the following is not an electromagnetic wave:
radio, television, blue light, infrared light, or sound?
4. What does it mean when your local disc jockey says,
that “you are listening to radio 1380”?
1. Two long straight wires carry identical currents in opposite
directions, as shown. At the point labeled A, is the direction of
the magnetic field left, right, up, down, into the page or out of
the page?
A.
2. A magnet produces a magnetic field that points vertically
upward. Along what line does the force on a proton act if it
enters this region with a horizontal velocity toward the south?
3. A copper ring is oriented perpendicular to a uniform magnetic
field. The ring is quickly stretched such its radius doubles over a
short time. As the ring is being stretched, is the magnitude of the
net magnetic field in the center of the loop greater than, equal to,
or less than the magnitude of the uniform field? Explain.
4. Can you accelerate the stationary particle with magnetic field?
An electric field? Explain.