CHEM 14A - Atom/Photoelectric stuff

module concept Qs

In a photoelectric experiment light hits a metal surface and if the energy of the ________ light is ________ enough it causes electrons to be ejected from the metal surface.

A. outgoing, large

B. outgoing, small

C. incoming, large

D. incoming, small

E. None of the above

C. incoming, large

. Does the photoelectric experiment need to be done under a vacuum?

A. No, as it would be harder to accelerate them and make them stay on path.

B. Only at night.

C. It depends.

D. Yes, otherwise the ejected electrons interact with molecules in the air.

D. Yes, otherwise the ejected electrons interact with molecules in the air.

Are electrons always ejected? Justify your answer.

A. Yes, electrons are always ejected.

B. Yes, if the incoming light has insufficient energy then electrons are ejected.

C. No, if the incoming light has insufficient energy then no electrons are ejected.

D. No, no electrons will be ejected under any conditions

E. None of the above

C. No, if the incoming light has insufficient energy then no electrons are ejected.

17. If long wavelength light is not ejecting electrons from a metal surface will increasing the intensity of the light result in electrons being ejected? Justify your answer.

A. No, because in this experiment light is not acting like a wave. If light were acting like a wave then the intensity would be proportional to the size (amplitude) of the wave and the bigger the wave the greater its energy.

B. No, because decreasing the intensity of the light increases the number of electrons being ejected.

C. Yes, because of increasing the intensity of the light increases the number of electrons being ejected.

D. Yes, because in this experiment light is acting like a wave.

E. None of the above

A. No, because in this experiment light is not acting like a wave. If light were acting like a wave then the intensity would be proportional to the size (amplitude) of the wave and the bigger the wave the greater its energy.

18. In the photoelectric effect what condition must occur for an electron to be emitted from a metal surface?

A. E (photon) > 0

B. E (photon) < E (remove e-)

C. E (photon) = E (remove e-)

D. E (photon) > E (remove e-)

E. C and D

E. C and D

19. Which one of following is not describing the photoelectric effect?

A. E (photon) – E (remove e-) = E (excess)

B. E (photon) – E (remove e-) = EK (e-)

C. hv - work function = 1/2mv²

D. λv = c

E. None of the above

D. λv = c

20. What was the photoelectric experiment originally designed to do?

A. Measure how much energy is required to remove an electron from a metal surface.

B. Measure how much energy is required to add an electron to a metal surface.

C. Measure how much free energy is released to remove an electron from a metal surface.

D. Measure how much free energy is released to add an electron to a metal surface.

E. None of the above

A. Measure how much energy is required to remove an electron from a metal surface.

21. What was the surprising outcome of the initial photoelectric experiments?

A. If electrons were ejected decreasing the light intensity resulted in no ejected electrons.

B. If electrons were ejected increasing the light intensity resulted in no ejected electrons.

C. If no electrons were ejected decreasing the light intensity resulted in ejected electrons.

D. If no electrons were ejected increasing the light intensity still resulted in no ejected electrons.

E. None of the above

D. If no electrons were ejected increasing the light intensity still resulted in no ejected electrons.

22. If no electrons are ejected what experimental change is needed?

A. Use shorter wavelength or higher frequency light.

B. Use shorter wavelength or lower frequency light.

C. Use longer wavelength or higher frequency light.

D. Use longer wavelength or lower frequency light.

E. None of the above

A. Use shorter wavelength or higher frequency light.

To interpret the results of photoelectric experiments the model of light needs to change from a ________ model to a ________ model. What are the two missing words?

A. particle, wave

B. particle, interaction

C. wave, particle

D. wave, photon

E. None of the above

C. wave, particle

24. In photoelectric experiments, typically what part of the electromagnetic spectrum is the incoming light?

A. Ultraviolet

B. Infrared

C. Visible light

D. Gamma rays

A. Ultraviolet

Choose the right description for the experimental setup in a spectroscopic experiment using a sample of hydrogen gas atoms as an example.

A. Light with many wavelengths is shone on the hydrogen sample. A detector measures wavelengths of light which are absorbed or emitted by the hydrogen atoms.

B. Light with many wavelengths is shone on the hydrogen sample. A detector measures the wavelengths of reflected light.

C. Light with many wavelengths is shone on the hydrogen sample. A detector measures the frequencies of light absorbed or emitted which vary due to the different speeds of the hydrogen atoms.

D. Light with many wavelengths is shone on the hydrogen sample. A detector measures the wavelengths of scattered light.

A. Light with many wavelengths is shone on the hydrogen sample. A detector measures wavelengths of light which are absorbed or emitted by the hydrogen atoms.

13. In the above experiment if only the absorbed wavelengths of light are detected what is the experiment called? What is the spectrum called?

A. Atomic absorption spectroscopy; Emission line spectrum

B. Atomic emission spectroscopy; Absorption line spectrum

C. Atomic absorption spectroscopy; Absorption line spectrum

D. Atomic emission spectroscopy; Emission line spectrum

C. Atomic absorption spectroscopy; Absorption line spectrum

14. In the above experiment if only the emitted wavelengths of light are detected what is the experiment called? What is the spectrum called?

A. Atomic absorption spectroscopy; Emission line spectrum

B. Atomic emission spectroscopy; Absorption line spectrum

C. Atomic absorption spectroscopy; Absorption line spectrum

D. Atomic emission spectroscopy; Emission line spectrum

D. Atomic emission spectroscopy; Emission line spectrum

15. In the above spectroscopic experiment what is the most unique characteristic of the observed results? Hint: What does a typical spectrum look like?

A. All wavelengths of light are absorbed or emitted. Spectrum consists of lines.

B. No wavelengths of light are absorbed or emitted. Spectrum consists of waves.

C. Only specific wavelengths of light are absorbed or emitted. Spectrum consists of lines.

D. Only specific wavelengths of light are absorbed or emitted. Spectrum consists of waves.

C. Only specific wavelengths of light are absorbed or emitted. Spectrum consists of lines.

19. When we say hydrogen atoms absorb a specific wavelength of light what do we mean? Use energy in your detailed explanation of what is being excited.

A. We mean that a photon with a specific energy lowers the energy of the electron in the hydrogen atom to its ground state. That is, the photon's energy matches the energy difference between two electronic energy levels.

B. We mean that a photon with a specific energy absorbs the energy of the electron in the hydrogen atom to a higher energy level. That is, the photon's energy matches the energy product of the two electronic energy levels.

C. We mean that a photon with a specific energy excites the electron in the hydrogen atom to a lower energy level. That is, the photon's energy matches the energy sum of two electronic energy levels.

D. We mean that a photon with a specific energy excites the electron in the hydrogen atom to a higher energy level. That is, the photon's energy matches the energy difference between two electronic energy levels.

D. We mean that a photon with a specific energy excites the electron in the hydrogen atom to a higher energy level. That is, the photon's energy matches the energy difference between two electronic energy levels.

23. When the frequency of a photon matches the energy difference between two electronic energy levels it is called the __________ frequency condition as described by the equation __________ where v is the __________, ∆E is the __________, and h is __________.

A. Bohr, v = ∆E/h, frequency of the absorbed light, energy difference between the electronic energy levels, Plank constant

B. Boltzmann, v = ∆E/h, velocity of the absorbed light, energy difference between the atomic energy levels, Plank constant

C. Planck, h = ∆E/v, frequency of the absorbed light, energy difference between the electronic energy levels, Boltzmann constant

D. Rutherford, v = ∆E/h, wavelength of the absorbed light, energy difference between the minimum and maximum energy levels, Plank constant.

A. Bohr, v = ∆E/h, frequency of the absorbed light, energy difference between the electronic energy levels, Plank constant