HW03-solutions

# HW03-solutions - vasquez(mpv244 HW03 Atomic Theory Part I...

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vasquez (mpv244) – HW03: Atomic Theory Part I – shear – (52375) 1 This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. Note the due date is Tuesday so you will get an answer key to study for the exam. A second homework will be posted tonight. 001 10.0 points Which color in the rainbow has the longest wavelength? 1. green 2. yellow 3. orange 4. red correct 5. blue Explanation: Ordered by wavelengths, blue < green < yellow < orange < red 002 10.0 points What is the correct order of decreasing en- ergy? 1. microwaves, visible light, x-rays, γ -rays, ltraviolet light 2. microwaves, visible light, ultraviolet light, x-rays, γ -rays 3. visible light, microwaves, x-rays, γ -rays, ltraviolet light 4. γ -rays, x-rays, ultraviolet light, visible light, microwaves correct 5. visible light, ultraviolet light, microwaves, x-rays, γ -rays Explanation: γ -rays > x-rays > ultraviolet light > visible light > microwaves 003 (part 1 of 2) 10.0 points When sodium is heated, a yellow spectral line whose energy is 3 . 37 × 10 - 19 J/photon is produced. What is the frequency of this light? 1. none of above 2. 6 . 626 × 10 - 34 Hz 3. 1 . 602 × 10 - 19 Hz 4. 5 . 09 × 10 14 Hz correct 5. 3 . 0 × 10 8 Hz 6. 5 . 09 × 10 - 34 Hz 7. 3 . 37 × 10 11 Hz 8. 3 . 37 × 10 19 Hz 9. 5 . 9 × 10 - 7 Hz Explanation: E photon = 3 . 37 × 10 - 19 J / photon ν = ? E photon = h ν ν = E photon h = 3 . 37 × 10 - 19 J 6 . 626 × 10 - 34 J · s = 5 . 09 × 10 14 Hz 004 (part 2 of 2) 10.0 points What is its wavelength? 1. 6 . 626 × 10 - 34 m 2. none of above 3. 1 . 602 × 10 - 19 m 4. 3 . 0 × 10 8 m 5. 5 . 09 × 10 14 m 6. 5 . 9 × 10 - 7 m correct Explanation: λ = ? c = λ ν

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vasquez (mpv244) – HW03: Atomic Theory Part I – shear – (52375) 2 λ = c ν = 3 . 0 × 10 8 m/s 5 . 09 × 10 14 Hz λ = 5 . 9 × 10 - 7 m 005 10.0 points What key result from the photoelectric effect showed that classical physics did not work on the atomic scale? 1. Light intensity and electron current were related. 2. All metals are reflective. 3. Different metals showed different behav- iors. 4. Radiation below a certain frequency, no matter how intense, would not cause electron emission. correct 5. The effect is not observed when a gas is introduced into the vacuum chamber. Explanation: When electromagnetic radiation (light) of sufficient minimum energy strikes a metal cathode, electrons are knocked off its sur- face, travel to an anode, and form a current through a circuit. Two important observations were: 1) Electrons can be ejected only if the light is sufficiently energetic. Electron ejection is independent of time or intensity. The mini- mum energy varies by element. 2) The current increases with increasing intensity and is independent of color. Therefore, light is made up of photons, each having a particular amount of energy that can be transferred to an electron during a colli- sion. If the energy is equal to or greater than the amount needed to liberate the electron, it can escape to join the photoelectric current.
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