This preview shows pages 1–2. Sign up to view the full content.
http://session.masteringphysics.com/myct
Page 1 of 11
http://session.masteringphysics.com/myct
[
Assignment View
]
E
ð
lisfræ
ð
i 2, vor 2007
32. Electromagnetic Waves
Assignment is due at 2:00am on Wednesday, March 28, 2007
Credit for problems submitted late will decrease to 0% after the deadline has passed.
The wrong answer penalty is 2% per part. Multiple choice questions are penalized as described in the online help.
The unopened hint bonus is 2% per part.
You are allowed 4 attempts per answer.
Travelling EM Waves
Traveling Electromagnetic Wave
Learning Goal:
To understand the formula representing a traveling electromagnetic wave.
Light, radiant heat (infrared radiation), X rays, and radio waves are all examples of traveling electromagnetic waves. Electromagnetic waves comprise combinations of electric and magnetic fields
that are mutually compatible in the sense that the changes in one generate the other.
The simplest form of a traveling electromagnetic wave is a plane wave. For a wave traveling in the
x
direction whose electric field is in the
y
direction, the electric and magnetic fields are given by
,
.
This wave is linearly polarized in the
y
direction.
Part A
In these formulas, it is useful to understand which variables are
parameters
that specify the nature of the wave. The variables
and
are the __________ of the electric and magnetic fields.
Hint A.1
What are parameters?
Hint not displayed
Choose the best answer to fill in the blank.
ANSWER:
maxima
amplitudes
wavelengths
velocities
Part B
The variable
is called the __________ of the wave.
Choose the best answer to fill in the blank.
ANSWER:
velocity
angular frequency
wavelength
Part C
The variable
is called the __________ of the wave.
Choose the best answer to fill in the blank.
ANSWER:
wavenumber
wavelength
velocity
frequency
Part D
What is the mathematical expression for the electric field at the point
at time
?
ANSWER:
Part E
For a given wave, what are the physical variables to which the wave responds?
Hint E.1
What are independent variables?
Hint not displayed
ANSWER:
only
only
only
only
and
and
and
and
This is a plane wave; that is, it extends throughout all space. Therefore it exists for any values of the variables
and
and can be considered a function of
,
,
, and
. Being an infinite
plane wave, however, it is independent of these variables. So whether they are considered independent variables is a question of semantics.
When you appreciate this you will understand the conundrum facing the young Einstein. If he traveled along with this wave (i.e., at the speed of light
), he would see constant electric and
magnetic fields extending over a large region of space with no time variation. He would not see any currents or charge, and so he could not see how these fields could satisfy the standard
electromagnetic equations for the production of fields.
[
Print
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview. Sign up
to
access the rest of the document.
 Spring '09
 All

Click to edit the document details