The Quantum Nature of L1ght

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] 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 Mark 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] 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] © NewOCR.com 2009 - 2017