Physics 1230
Homework 5
Due Monday. June 13, 2016
This homework covers material on how light is created by incandescence (making things
hot) and luminescence (adding energy to and releasing energy from the discrete energy
levels of atoms and molecules). We also are now heading into learning about the
behavior of mirrors and lenses.
1. Incandescent light bulbs. (12 points total)
(a) Use Wien’s Law to calculate the peak wavelength at which an incandescent lamp
filament with a temperature of 2900 K radiates its maximum power. Show your
work. (3 points)
(b) Is wavelength of the peak radiation visible to the eye? (3 points)
(c) Based on the above, explain why is a standard incandescent light bulb typically
felt to be inefficient as a light source. (3 points)
(d) Based on the above, explain why standard incandescent light bulbs look more
warm, or "orange" than sunlight? (3 points)
Physics 1230
HW5.1
Summer 2016
Physics 1230
Homework 5
Due Monday. June 13, 2016
2. Energy levels in atoms and light as photons. (8 points total)
a) We normally talk about light as having a color, or for the light frequencies that we
cannot see, a wavelength or type of light. We now know that electromagnetic
waves can also be described as streams of photons. When atoms and molecules
release energy, it is observed to come out in ‘photons’ where each photon carries
an energy that is proportional to the frequency of the type of light. List the
following in order from LOWEST to HIGHEST energy per photon: Green, blue,
red, x-ray, gamma ray, infrared. (4 points)
b) In airports now you will find ‘millimeter wave’ scanners. Google millimeter
wave scanner to learn a bit more and then explain: What part of the spectrum is
it in – express your answer as an approximate range in Hz and in scientific
notation. Is it ionizing or non-ionizing radiation? How would you convince a
friend it is a safe scanning mechanism? (4 points)
Physics 1230
HW5.2
Summer 2016
Physics 1230
Homework 5
Due Monday. June 13, 2016
3. More about the energy levels of electrons in atoms. (4 points) Below is a model of
the energy levels in an atom. For this particular type of atom, an electron emits a blue
photon when it loses energy and goes from E3 to E1.
TRUE or FALSE (circle one) It is possible that an electron moving from E4 to E1
will emit a red photon.
4. Specular vs. diffuse reflection (6 points total)
a) Look around you right now and name 3 things that you see due to specular
reflection, and 3 due to diffuse reflection. (3 points)
b) TRUE or FALSE (circle one): Specular and diffuse reflection are
fundamentally different and follow different rules of reflection when light rays are
specularly or diffusely scattered.
Physics 1230
HW5.3
Summer 2016