Chapter 22: Electromagnetic Waves Flashcards
The basic equations governing electromagnetism were compiled by ________
Maxwell
An electric field is produced by a ________
changing magnetic field
A changing electric field will produce a ________
magnetic fields
Electromagnetic waves travel through a vacuum at ________
the same speed regardless of their frequency.
In a vacuum, the velocity of all electromagnetic waves ________
is nearly 3 x 10^8 m/s.
The E and B fields in electromagnetic waves are oriented ________
perpendicular to the wave’s direction of travel, and also to each other.
Electromagnetic waves are ________
transverse
Of the following, which is not electromagnetic in nature?
sound waves
Visible light ranges in wavelength from ________
400 nm to 750 nm.
The energy an electromagnetic wave transports per unit time per unit area is the ________
intensity
Which of the following correctly lists electromagnetic waves in order from longest to shortest wavelength?
radio waves, infrared, visible light, x-rays
What is the wavelength of light waves if its frequency is 5.0 x 10^14 Hz?
0.60 µm
What is the wavelength of a 92.9-MHz radio wave?
3.23 m
What is the frequency of 20 mm microwaves?
15 GHz
How long does it take the signal from a local radio station to travel 20 miles?
107 µs
How far is a light year (the distance light travels in a year)?
9.5 x 10^15 m
Estimate the average power output of the Sun, given that about 1350 W/m2 reaches the upper atmosphere of the Earth and the distance from the Sun to the Earth is 1.5 x 10^11 m.
4 x 10^26 W
Radiation from the Sun is about 1000 W/m2. What would be the pressure due to the Sun on a reflective sheet 10 m^2 in area?
6.7 x 10^-6 N/m^2
electromagnetic (EM) wave
The net result of this chain of events is the production of a wave made of oscillating electric and magnetic fields
The electric field in an EM wave traveling northeast oscillates up and down. In what plane does the magnetic field oscillate?
in the NW-SE plane
An electromagnetic wave is propagating toward the west. At a certain moment, the direction of the magnetic field vector associated with this wave points vertically up. What is the direction of the electric field vector?
Horizontal and pointing south
If the magnetic field in an EM wave has a peak magnitude of 12.5 nT, what is the peak magnitude of the electric field?
What is the frequency of a microwave whose wavelength is 1.50 cm?
An FM radio station broadcasts radio waves at a frequency of 96.7 MHz. What is the wavelength associated with this broadcast?
3.1 m
The magnetic field in a traveling EM wave has an rms strength of 22.5 nT. How long does it take to deliver 335 J of energy to 1.00 cm2 of a wall that it hits perpendicularly?
(a) Estimate the radiation pressure due to a 75-W bulb at a distance 8.0 cm from the center of the bulb.
(b) Estimate the force exerted on your
fingertip if you place it at this point.
amplitude modulation
amplitude of the high frequency
carrier signal varies in proportion to the amplitude of the audio signal
frequency modulation
frequency of the carrier wave
varies in proportion to the audio amplitude
Before the days of cable, televisions often had two antennae on them, one straight and one circular. Which antenna picked up the magnetic oscillations?
the circular one
