Download P114 PROBLEM SET 9 Spring 2014

P114
PROBLEM SET 9
Spring 2014
Homework to be handed in by 1700 hours on 8 April 2014.
[1] A penny weighs 2.0 g. Calculate the rest energy for a penny. If you convert this energy completely to electrical
energy and sell it at 10 cent/kW-hour, how much money will you make?
[2] Your friend, who is exactly the same age as you, travels at a speed of 0.9990c to a star 25 light-years away. She
spends 10 years on one of the star’s planets and then returns at 0.999c.
(a) How long has she been away as measured by you?
(b) How long does she measure for the time she is away?
[3] When light of wavelength 300 nm is incident upon potassium, the emitted electrons, due to the photoelectric
effect, have a maximum kinetic energy of 2.03 eV.
(a) What is the energy of the incident photon?
(b) What is the work function for potassium?
(c) What would be the stopping potential if the incident light had a wavelength of 430 nm?
(d) What is the threshold wavelength for the photoelectric effect with potassium?
[4] A hydrogen atom is in its tenth excited state according to the Bohr model (n=11).
(a) What is the radius of the Bohr orbit?
(b) What is the angular momentum of the electron?
(c) What is the electron’s kinetic energy?
(d) What is the electron’s potential energy?
(e) What is the electron’s total energy?
[5] A certain radio station broadcasts at a frequency of 10 MHz with an average power output of 5 kW.
(a) What is the energy of a photon in electronvolts?
(b) How many photons does the station emit per second?
(c) Why are quantum effects not observed in radio transmission at this frequency?
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