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1. Which experiments resulted in observations which showed that:
a) cathode rays originate at the anode.
b) cathode rays travel in straight lines.
c) cathode rays carry energy and can therefore do work.
d) the nature of the charge of cathode rays is negative.
2. The diagram below has an arrow which shows the direction of movement of a beam of
electrons. For the following situations, what is the direction of deflection of this beam?
a) Object A has a negative charge on it.
b) Object B has a positive charge on it.
c) Object A is a south pole of a magnet and object B is a north pole of a magnet.
3. Cathode rays are deflected by a magnetic field. The beam will remain narrow even after
deflection. Explain what observations would be made when the following changes occur.
a) The beam is made of particles with differing negative charges, but all the particles have
the same mass.
b) The particles in the beam all have the same negative charge, but the particles differ
in mass.
c) The particles in the beam have masses that are proportional to the charge. For
example, if the mass of a particles is double the mass of another particle, then the charge
will be double the charge of the other particle.
4. A charged particle is moving at a speed of 6.0 X 106 m/s. The particle is moving
perpendicular to a uniform magnetic field with an intensity of 3.2 X 10-2 T. As a result, the
particle moves in a circular path of radius 1.8 cm. What is the charge-to-mass ratio for the
particle?
5. Determine the velocity of a proton which is moving perpendicular to a uniform magnetic field
with magnitude 1.8 T, if the radius of the path is 3.0 cm. Remember that the mass of the
proton is 1.67 X 10-27 kg.
6. A beam of electrons in a cathode ray tube produces a dot on the screen at the end of the tube.
What changes to the dot would occur if
a) the heater wire is made hotter by passing more current through it?
b) the potential difference between the anode and cathode is increased?
c) the charge on the control electrode is made more negative?
7. Similar technologies are used with radar and sonar. A cathode ray tube is used to display the
locations of objects relative to the radar or sonar station. What are other similarities and
differences between these two applications of a cathode ray tube?
8. For each of the following situations, what is the energy of the photon? Express your answers
in electron volts.
a) An X-ray has a frequency of 1.2 X 1018 Hz.
b) The wavelength of violet light is about 400 nm.
c) The frequency of the monochromatic red light from a laser is 4.4 X 1014 Hz.
d) Infrared light from a heat lamp has a wavelength of 900 nm.
9. A metal used in the photoelectric effect has a work function of 2.48 eV. The metal is
irradiated with light of wavelength 450 nm. What will be the maximum kinetic energy of the
emitted photoelectrons?
10. When black and white film is developed, a red light may be left on in the developing room.
Why doesn't the red light ruin the film?
11. Why does ultraviolet light cause sunburns, while infrared light only warms your skin?
12. Substance Work Function
sodium 2.26 eV
copper 4.46 eV
potassium 1.60 eV
barium 2.48 eV
a) When comparing sodium and copper, which requires more energy to cause
photo emission? Explain.
b) When comparing potassium and barium, which requires the higher minimum frequency
of light to cause photo emission? Explain.
13. A photon has a wavelength of 122 nm. This photon is from the ultraviolet region of the
electromagnetic spectrum. How much energy does this photon have. Answer in both Joules
and electron volts.
14. The average wavelength of visible light from the sun can be taken to be about 5.50 X 10-7 m.
In northern California, the average solar power striking the Earth's surface is about
1.0 kW/m2. For an area of 1.0 cm2, and assuming that light rays strike at 90o to the Earth's
surface, how many photons strike the Earth in northern California per second?
15. A metal surface has a work function of 2.46 eV. Determine the largest wavelength of light that
can cause the photoelectric effect.
16. The work function of a metal is 2.3 X 10-19 J. Light of wavelength 6.00 X 10-7 m is striking
this surface. What is the stopping voltage, and maximum kinetic energy for the emitted
photoelectrons?
17. The stopping voltage in a photoelectric experiment is 1.2 V. The light used in this experiment
has a wavelength of 480 nm. Calculate the work function for the material used in the
experiment.
18. For the Rutherford model of the atom, explain what keeps the electrons around the nucleus
of the atom.
19. For a given aiming error, alpha particles are scattered through angles of 135o. If the aiming
error is reduced, what range of angles will alpha particles be scattered through?
20. In the Rutherford scattering experiment, out of 12 000 alpha particles, only 5 scatter through
angles larger than 5o. Given the following changes, out of 12 000 alpha particles, what
number would be scattered through angles larger than 5o?
a) Foil thickness is doubled.
b) Foil thickness is increased by a factor of 100.
21. The gold atom has a charge of +79 e on it. Alpha particles (mass = 6.6 X 10-27 kg) are
accelerated to energies of 4.5 MeV, and then directed at a gold foil. How close to the gold
nucleus can these alpha particles come?
22. Aluminum has an atomic number of 13, while gold's atomic number is 79. If alpha particles
with the same energy approach aluminum and gold foils, how much closer will the alpha
particles come to the aluminum nuclei, than to the gold nuclei?
23. The wavelengths of three lines in an emission spectrum are 172 nm, 194 nm, and 258 nm.
These lines represent transitions from higher states to ground state.
a) What are the energies of these excited states?
b) What are the wavelengths of three other lines in the spectrum of this substance?
24. A sodium atom can emit a photon with a wavelength of 589 nm. What energy difference
exits between the energy levels that produce this photon?
25. Calculate the energy loss of an atom which emits a photon with a wavelength of
6.84 X 10-7 m.
26. An electron in a hydrogen atom moves from the second energy level to the sixth. What is the
wavelength and frequency of the absorbed photon?
January 20, 2014
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