Homework 1
(1) Write a “Dear Dr. Mike” letter, telling me a little about yourself. What are you majoring in, what are your interests in life, and what do you want to learn in this class? (Type this and turn it in on paper; somewhere between 1/2 and 1 page in length, double-spaced).
NOTE: For the following problems, show your math calculations for full credit:
(2) Most cell phones used in the US transmit on a microwave frequency of 1900 MHz. What is the wavelength (in centimeters) of the EM waves emitted by your cell phone?
(3) Internet information is sent over optical fibers using near-infrared lasers operating between 1500 – 1600 nm in wavelength. What is the frequency of a laser that emits at 1550nm?
(Quote your answer in Hz, using scientific notation: i.e. ___ x 10— Hz)
(4) “When a laser beam is sent to the moon, reflected there, and returned to earth, it takes 2.5 seconds for the round trip. Calculate the distance to the moon.” (this is Problem PM2, on page 26 of our “STL” textbook).
(5) There is often a noticeable (annoying?!) time delay between the question asked by someone in a TV studio and the start of the answer given by a reporter in some remote location. Most likely, this is due to the use of a relay-satellite making the microwave radio connection. These satellites are located in geostationary orbit, 22,236 miles (= 35,785 km) directly above the Earth’s equator.
- Calculate the time it takes a microwave signal to travel from the TV station to the reporter.
- Does this account for the time delay you often observe while watching TV (≈ 2 sec)?
(6) Use the values of the “ChemCam” on the Mars Curiosity Rover to calculate the power density blasted onto a Mars rock. Assume: pulse width = 5 ns, energy/pulse = 15 mJ, laser spot diameter = 0.5mm. Quote your answer in MW/mm2.
(a) What is your calculated power density, in MW/mm2 ?
(b) Is it high enough to vaporize a Martian rock? (> 10MW/mm2 ?)
NOTE: For problems (4) and (5), you need the following equation, that relates the speed of light (c) to distance (d) and time (t):
