Download Session 27- Power in EM Waves

Session 27: Power in EM
Waves
Supplemental Instruction
Iowa State University
Leader:
Course:
Instructor:
Date:
Garrett Schieber
Phys 222
Dr. Al-Saqer
11/12/14
Warm-up
1) At a distance of 8.5 km from a radio transmitter, the amplitude of the oscillating electric field
in the radio wave is Eo = 0.13 V/m. What is the maximum value of the energy-density of the
electromagnetic field at this location (in J/m3)?
a) 7.5 x 10-14
b) 3.0 x 10-13
c) 4.5 x 10-5
d) 2.2 x 10-5
e) 1.5 x 10-13
2) A standing electromagnetic plane wave is given by
𝜋
3𝜋
𝑬(𝑥, 𝑡) = 𝑗̂cos⁡( 𝑥 −
∗ 108 𝑡)
2
2
where x is in meters, t in seconds, and all angles are in radians. What is the wavelength (in
m) of the wave?
a) 2 m
b) 1.27 m
c) 12.6 m
d) 4 m
e) 1.0 m
Team Activity
3) An intense light source radiates uniformly in all directions. At a distance of 5.3 m from the
source the radiation pressure on a perfectly absorbing surface is 7.5×10−6 N/m2. What is the
average power output of the source? (Book 32.25)
Supplemental Instruction
1060 Hixson-Lied Student Success Center  294-6624  www.si.iastate.edu
Challenge Problem:
4) A sinusoidal electromagnetic wave from a radio station passes perpendicularly through an
open window that has area of 0.600 m2. At the window, the electric field of the wave has an
rms value 2.20×10−2 V/m. How much energy does this wave carry through the window
during a 30 s commercial? (Book 32.18)
5) A plane electromagnetic wave with wavelength λ is given by:
What is the magnitude and direction of the amplitude of the B-field B0 if the wave is traveling
in the –y direction?
a. 6.7 * 10-9 T in the + x direction
b. 6.7 * 10-9 T in the - x direction
c. 1.5 * 10-7 T in the + x direction
d. 1.5 * 10-7 T in the - x direction
e. 2.1 * 10-6 T in the + x direction