**Examples for electromagnetic
waves**

Example #1

Problem:

a.) If a radio station broadcasts at 88.9 *MHz*,
what is the wavelength of the signal?

Solution:

Use * l* =

l = 3.37 *m*

b.) How long does it take sunlight to reach
the earth? DATA: **R**_{earth's orbit}* *=
1.5 E8

Solution:

The time is given by:* t* =

* t*
= 500

Example #2

Problem:

A satellite emits a radio signal with an
average power of 1000 *W*. The signal is spread evenly in all directions. What is
the *rms* strength of the electric field from the radio wave, when one is three
million *km* away.

Solution:

First, calculate the intensity of the light, with = 1.1 E-16 *W/m*^{2}.

Next, calculate the Electric field strength using .

E* *=
2.89 E-7

Example #3

Problem:

a.) Light of an intensity of 100 *W/m*^{2},
directed along the * z* axis and polarized along the

Solution:

The cosine of 90 degrees is zero.

S_{ave} = 0 *W/m ^{2}*

b.) For the same problem as above, suppose
one uses 2 polarizers, one oriented midway between the * x *and

Solution:

The cosine of 45 degrees is 1/sqrt(2), so each polarizer cuts out half the intensity.

S_{ave} = 25 *W/m ^{2}*

c.) For the same problem as above, suppose one uses 90 ideal polarizers, each one oriented one degree past the preceeding one.

Solution:

The fraction that comes through will be **cos( 1.0
degrees) ^{180}**.

S_{ave} = 97 *W/m ^{2}*