# Physics 101

## Home Works

• Homework 10.(due Friday, Dec. 5). Click here for the pdf file.
• Homework 9 (due Friday, Nov. 19).
1. See pages 433 - 439 of the text book. What is the longest wavelength and and shortest wavelength expected from the Lyman series and also from the Blamer series of the hydrogen atom.
2. For the n-th level hydrogen atom, calculate the radius of the electron orbit and the velocity of the electron as functions of n.
3. Problem 28.14

• Homework 8 (due Friday, Nov. 12).
1. Calculate the wavelengths of radio waves with 0.9 mhz (AM), 100 mhz (FM), 1,000 mhz (your cell phone).
2. A FM broadcasting station is emitting radio waves of 100 mhz with output power of 100 megawatts. What is the photon energy? How many photons are emitted per second?
3. Problem 26.8. Assume the wavelength of the sunlight is 600 nanometers.

• Homework 7 (due Friday, Nov. 5).
1. The speed of electron around the proton is c/137 in hydrogen atom, where c is the speed of light. Calculate the radius of the electron orbit.
2. In TV picture tubes, electrons are accelerated from zero velocity by two metal plates whose voltage difference is 30,000~Volts. What is the kinetic energy of the electrons? What is the speed of those electrons?
3. In the United States, the standard household voltage is 120 V. If your iron draws the electric power of one KW, what is the current through the heating coil? What is the resistance of the coil. If you bring the same iron to Europe where the standard voltage is 220 V, What would be current, and power?

• Homework 6 (due Friday, Oct.22).
Problem 1. Explain how air conditioners work in terms of the heat of vaprization. Explain also how heat pumps work.
Prob. 22.1, 22.6.

• Homework 5 (due Friday, Oct. 15). Assuming that your mass is 60Kg, calculate the energy (in joules) to climb the hill 100 meters high. Calculate in Calories. Do you know how many Calories (from food) you need to live for one day. Compare this number with the energy need to climb the hill.
Probs. 17.22, 17.24.

• Homework 4 (due Friday, Oct. 8). It takes 30 days for the moon to circle around the earth. Calculate the distance to the moon from the center of the earth.
Problem 16.2, Problem 17.8.

Homework 3 (due Friday, Oct. 1). Exam I

• Homework 3 ( due Friday, Sept. 24). Probs. 9.13, 9.15, and 10.6.

• Homework 2 ( due Friday, sept. 17). Probs. 8.1, 8.2, and 8.4.

• Homework 1 (due Friday, Sept. 10). We discussed in class how to measure the height of a tower, but there is an alligator-infested swamp between you and the tower. Write up what we discussed in a coherent and logical manner.