Electromagnetic Waves Flashcards
Polaris Aa, also known as the North Star, is a yellow supergiant about 100 parsec (pc) from our solar system. A parsec is approximately 3.0857 x 1016 meters. When looking at the North Star in the night sky, how long ago was the light that you are observing emitted? (Note that a year is approximately 3.154 x 107 seconds.)
From the information given, we can first convert the distance to Polaris Aa to meters: (1 x 102 pc)(3 x 1016 meters/pc) = 3 x 1018 meters to Polaris Aa
We can then determine how long light would take to reach us from Polaris Aa:
(3 x 1018 meters)/(3 x 108 m/s) = 1 x 1010 seconds for light to travel
Finally, we can convert that time into our desired units, years:(1 x 1010 seconds)/(3 x 107 seconds/year) = 0.33 x 103 years = 330 years
The rapid decay of 270-Darmstadtium to Hassium-266 has been observed to emit an alpha particle and be accompanied by the emission of a photon with 218 KeV energy. What is the wavelength of the emitted photon and what type of radiation is this? (Note that an electronvolt is equivalent to 1.6 x 10-19 Joules.)
To answer this, we need to recollect 2 pieces of information. First, the expression for the energy of a particle, which is E = hf. Second, we will need the frequency-wavelength relationship, or c = λf. Finally, we need two combine these two into one expression, yielding:
E = hc/λ
Solving for wavelength, we get:
λ = hc/E
Now we can convert the given energy into Joules:
(2.2 x 105 eV)(1.5 x 10-19 J/eV) = 3.3 x 10-14 J
It is worth taking a pause to look at our expression for the ultimate solution, λ = hc/E, before plugging in numbers. A quick check for intuition reveals that this makes sense - the energy carried by a wave is inversely proportional to its wavelength. Now we can plug in and get:
(3 x 108 m/s)(6.6 x 10-34 J•s)/(3.3 x 10-14 J) = (20 x 10-26 J•m)/(3.3 x 10-14 J) = 6 x 10-12 meters
Steve has a fancy fiber optic connection directly to a server, meaning that a single cable runs directly from him to the server. He has a ping, or round-trip time for a single piece of information, of about 4 milliseconds. Assuming this round trip time is entirely due to the traveling velocity of the signal and that the speed of light in a fiber optical cable is reasonably close to that of light in a vacuum, how far away is the server?
(You may consider just the surface distance, ignoring curvature of the Earth)
The total distance traveled by a single piece of information is simply velocity multiplied by time. However, the distance to the server is only half the distance that the signal travels, as the signal covers this distance twice to complete a round trip. Therefore, we can calculate distance to the server in the following way:
distanceserver = (c)(t/2) = (3 x 108 m/s)(2 x 10-3s) = 6 x 105 meters
So 600000 meters, or 600 km.
Which of the following never changes when going from one media to another? Wave Frequency Wave Speed Amplitude Wavelength
FREQUENCY NEVER CHANGES!
How do you calculate the velocity of a wave?
V=lambda*f
Velocity=wavelength * frequency
Describe what a period is in periodic motion?
Time between consecutive impulses. T=1/frequency.
The wave period is the time it takes to complete one cycle. The standard unit of a wave period is in seconds, and it is inversely proportional to the frequency of a wave, which is the number of cycles of waves that occur in one second. In other words, the higher the frequency of a wave, the lower the wave period.
Place the following in order of shortest to longest wavelength: Long Radio Vis UV Gamma X Radio Micro
Gamma, X, UV, Vis, IR, Micro, Radio, Long Radio
How many nm: Blue light
475
How many nm: Red light
625-700 ish
How many nm: Green light
530
What is the range in nm of the visible light spectrum?
400nm-700nm
Violet-Red
