0 Please answer the questions on these pages. You can attach additional
pages if you need more space. If you do then please clearly indicate which
question is being answered on the extra page. This assignment is out of 20
marks.
Marker General Comments
Download
Google Translate
Bing Translator
Edit Online
NATS 1720
NAME:
ASSIGNMENT 7
The Quantum Nature of Light
Due: Mar 16, 2017
• Please answer the questions on these pages. You can attach additional
pages if you need more space. If you do then please clearly indicate which
question is being answered on the extra page. This assignment is out of 20
marks.
• Your completed assignment is to be handed in at the NATS 1720 drop-box
outside Bethune 218 by no later than 4pm on Thursday, March 16th.
Marker General Comments
NATS 1720
NAME:
1. Small hand-held sensors are now routinely used to measure the surface temperature
of interior windows and walls to aid in the search for sources of heat loss in homes.
Explain how you think these sensors probably work. [2 Marks]
2. A red glow becomes just barely visible in steel when its temperature reaches 460? C.
As the temperature continues to increase the red glow of course becomes brighter.
a) Treating the steel as a blackbody, at what wavelength does it glow most brightly
at 460? C? Is this wavelength in the visible part of the EM spectrum? [1 Marks]
b) Taking the answer to part a) into consideration, why can we see a red glow from
steel with the naked eye at that temperature? [2 Mark]
NATS 1720
NAME:
3. The interior of a small lunchbox is lined with silvered reflective material that helps to
keep a hot lunch hot and a cold one cold. Similarly, the exterior of space satellites
is routinely covered in a reflective foil-like material to help keep the interior of the
spacecraft at a relatively constant temperature. (For context, the temperature outside
of the space station varies from 121? C on the side facing the sun down to -157? C on
the dark side.) Explain, in your own words, how the lining of the lunch box and the
blanket around a satellite achieve their stated purposes. [4 Marks]
4. Use Einstein’s photon theory to estimate the energy (in electron-volts) carried by
photons with wavelengths 900 nm, 620 nm, and 30 nm, and identify which part of the
EM spectrum each corresponds to. (Use the fact that the product of Planck’s constant
and the speed of light, h × c = 1240 eV · nm.) [2 Marks]
5. Consider monochromatic light (light of a single wavelength) incident on black & white
photographic film. The incident photons will leave a mark if they have enough energy
to break apart the silver-bromide molecules in the film. The minimum energy required
to do this is about 0.62 eV. What is the cutoff wavelength greater than which the light
will not be recorded? In what part of the EM spectrum does this wavelength fall? [2
Marks]
NATS 1720
NAME:
6. Consider the energy level diagram shown below, where the energy of each level is given,
and answer the questions below:
2.09 eV
1.41 eV
0.27 eV
0.00
a) Supposing that electrons can jump from one state to another with no restrictions,
how many light-emitting transitions are possible and what are their associated
energies? (Draw labelled arrows on the diagram and list the labels and corresponding transition energies below.) [2 Mark]
b) How many of those transitions emit visible light? (Be sure to explain your reasoning.) [1 Marks]
c) Will the system for which this is the level diagram absorb light of wavelength
530nm? Explain. [1 Mark]
7. A 650 nm light source delivers a power (energy per second) of 20 milliwatts to a
surface. If the beam power is increased to 40 mW, what increases: the energy of
individual photons or the total number of photons? Explain. [1 Mark]
NATS 1720
NAME:
8. Explain roughly how Louis de Broglie’s postulate of matter waves provides a “natural”
explanation of Bohr’s quantized atomic electron orbits. [2 Marks]
PLACE THIS ORDER OR A SIMILAR ORDER TODAY AND GET AN AMAZING DISCOUNT 🙂
