If the wavelength λ associated with a photon is cut in half, the photon's energy E
- is cut in half
- is reduced by a factor of 4
- stays the same
+ becomes twice as big
- becomes 4 times as big
c=fλ is easy to remember because the dimensions are right. Since fλ is constant, f∝1/λ. E=hf is harder to remember, but leads to E∝f leads to E∝1/λ If wavelength goes down, energy goes up porportionally.
If the frequency f associated with a photon increases by a factor of 4, the photon's wavelength λ
- is cut in half
+ is reduced by a factor of 4
- stays the same
- becomes twice as big
- becomes 4 times as big
c=fλ is easy to remember because the dimensions are right. Since fλ is constant, f∝1/λ. If wavelength goes up a factor of 4, frequency goes down a factor of 4.
If a 3 eV photon strikes a metal plate and causes an electron to escape, that electron will have a kinetic energy that is
- zero
+ less than 3 eV
- equal to 3 eV
- greater than 3 eV
- equal to 6 eV
First the electron loses KE due to the work function. But also, the stopping voltage measures only the component of KE associated with motion perpendicular to the plate. It is the first consideration that guarantees an energy less than the photon's.
In the Phet lab for photoelectric effect, how was the electron's kinetic energy measured?
- measuring spin
- measuring polarization
- measuring both spin and polarization
- deflecting the electron with a magnetic field
+ stopping the electron with an applied voltage
Two black bodies of are created by cutting identical small holes in two large containers. The holes are oriented so that all the photons leaving one will enter the other. The objects have different temperature and different volume. Which object has the greater electromagnetic ("photon") energy density (energy per unit volume)?
+ The hotter object has a greater energy density.
- The larger object has a greater energy density.
- They have the same energy density (since the holes are identical).
- No unique answer exists because two variables are involved (temperature and volume).
This question serves two purposes: (1) to inform students that the "photon" first emerged as a solution to the blackbody problem, and (2) to introduce the distinction between intensive and extensive properties.
Two black bodies of are created by cutting identical small holes two large containers. The holes are oriented so that all the photons leaving one will enter the other. The objects have different temperature and different volume. Which object emits more photons per second (above a given threshold energy)?
+ The object with the greater temperature emits more.
- The object with the greater volume.
- They both emit the same number of photons (since the holes are identical).
- No unique answer exists because two variables are involved (temperature and volume).
We know that the emission spectrum of a black body depends only on temperature (with power also depending on area). Carnot's version of the second law of thermodynamics stipulates that photon energy must flow from the hotter to the colder object. By inserting filters between the two (identical) holes we can ensure that this equality holds at all wavelengths.
Two black bodies of are created by cutting identical small holes in two large containers. The holes are oriented so that all the photons leaving one will enter the other. The objects have different temperature and different volume. Which object has the greater electromagnetic ("photon") energy?
- The hotter object has a greater energy.
- The larger object has a greater energy.
- They have the same energy (since the holes are identical).
+ No unique answer exists because two variables are involved (temperature and volume).
To suppress blind memorization, this question is a partner to a similar one where the question was about energy density.
- Photons striking metal and ejecting electrons (photo-electric effect explained in 1905)
- Diffraction observed in light so faint that photons seemed to have no mechanism to interact with each other (observed in 1909)
- A system similar to the one that led to the 1901 proposal that light energy is quantized as integral multiples of hf (except that Plank assumed that the walls were conductive.)
+ Evidence presented in 1800 that light is a wave.
- The transfer of energy and momentum of a high energy photon of a nearly free electron.
This is the first of four questions that might not suit all instructors. One way to alleviate this is to look at whether a given question is on the test, and talk about that one. Informing students that the others will not be on the test will prevent memorization, but not informing them (and not talking about) will also disincentivize memorization and encourage lecture attendance.
- Photons striking metal and ejecting electrons (photo-electric effect explained in 1905)
+ Diffraction observed in light so faint that photons seemed to have no mechanism to interact with each other (observed in 1909)
- A system similar to the one that led to the 1901 proposal that light energy is quantized as integral multiples of hf (except that Plank assumed that the walls were conductive.)
- Evidence presented in 1800 that light is a wave.
- The transfer of energy and momentum of a high energy photon of a nearly free electron.
A candidate for the first "spooky" experiment of quantum mechanics?
+ Photons striking metal and ejecting electrons (photo-electric effect explained in 1905)
- Diffraction observed in light so faint that photons seemed to have no mechanism to interact with each other (observed in 1909)
- A system similar to the one that led to the 1901 proposal that light energy is quantized as integral multiples of hf (except that Plank assumed that the walls were conductive.)
- Evidence presented in 1800 that light is a wave.
- The transfer of energy and momentum of a high energy photon of a nearly free electron.
Students will likely memorize only one aspect of this answer. I put the most important first (physical process), and expect other questions on other quizzes to reinforce that it is called the photo-electric effect.
- Photons striking metal and ejecting electrons (photo-electric effect explained in 1905)
- Diffraction observed in light so faint that photons seemed to have no mechanism to interact with each other (observed in 1909)
+ A system similar to the one that led to the 1901 proposal that light energy is quantized as integral multiples of hf
- Evidence presented in 1800 that light is a wave.
- The transfer of energy and momentum of a high energy photon of a nearly free electron.
Plank assumed that the walls were perfect conductors, not exactly what is shown.
? If the wavelength λ associated with a photon is cut in half, the photon's energy E
- is cut in half
- is reduced by a factor of 4
- stays the same
+ becomes twice as big
- becomes 4 times as big
$ c=fλ is easy to remember because the dimensions are right. Since fλ is constant, f∝1/λ. E=hf is harder to remember, but leads to E∝f leads to E∝1/λ If wavelength goes down, energy goes up porportionally.
? If the frequency f associated with a photon increases by a factor of 4, the photon's wavelength λ
- is cut in half
+ is reduced by a factor of 4
- stays the same
- becomes twice as big
- becomes 4 times as big
$ c=fλ is easy to remember because the dimensions are right. Since fλ is constant, f∝1/λ. If wavelength goes up a factor of 4, frequency goes down a factor of 4.
? If a 3 eV photon strikes a metal plate and causes an electron to escape, that electron will have a kinetic energy that is
- zero
+ less than 3 eV
- equal to 3 eV
- greater than 3 eV
- equal to 6 eV
$ First the electron loses KE due to the work function. But also, the stopping voltage measures only the component of KE associated with motion perpendicular to the plate. It is the first consideration that guarantees an energy less than the photon's.
? Two black bodies of are created by cutting identical small holes in two large containers. The holes are oriented so that all the photons leaving one will enter the other. The objects have different temperature and different volume. Which object has the greater electromagnetic ("photon") energy density (energy per unit volume)?
+ The hotter object has a greater energy density.
- The larger object has a greater energy density.
- They have the same energy density (since the holes are identical).
- No unique answer exists because two variables are involved (temperature and volume).
$ This question serves two purposes: (1) to inform students that the "photon" first emerged as a solution to the blackbody problem, and (2) to introduce the distinction between intensive and extensive properties.
? Two black bodies of are created by cutting identical small holes two large containers. The holes are oriented so that all the photons leaving one will enter the other. The objects have different temperature and different volume. Which object emits more photons per second (above a given threshold energy)?
+ The object with the greater temperature emits more.
- The object with the greater volume.
- They both emit the same number of photons (since the holes are identical).
- No unique answer exists because two variables are involved (temperature and volume).
$ We know that the emission spectrum of a black body depends only on temperature (with power also depending on area). Carnot's version of the second law of thermodynamics stipulates that photon energy must flow from the hotter to the colder object. By inserting filters between the two (identical) holes we can ensure that this equality holds at all wavelengths.
? Two black bodies of are created by cutting identical small holes in two large containers. The holes are oriented so that all the photons leaving one will enter the other. The objects have different temperature and different volume. Which object has the greater electromagnetic ("photon") energy?
- The hotter object has a greater energy.
- The larger object has a greater energy.
- They have the same energy (since the holes are identical).
+ No unique answer exists because two variables are involved (temperature and volume).
$ To suppress blind memorization, this question is a partner to a similar one where the question was about energy density.
- Photons striking metal and ejecting electrons (photo-electric effect explained in 1905)
- Diffraction observed in light so faint that photons seemed to have no mechanism to interact with each other (observed in 1909)
- A system similar to the one that led to the 1901 proposal that light energy is quantized as integral multiples of hf (except that Plank assumed that the walls were conductive.)
- The transfer of energy and momentum of a high energy photon of a nearly free electron.
$ This is the first of four questions that might not suit all instructors. One way to alleviate this is to look at whether a given question is on the test, and talk about that one. Informing students that the others will not be on the test will prevent memorization, but not informing them (and not talking about) will also disincentivize memorization and encourage lecture attendance.
- Photons striking metal and ejecting electrons (photo-electric effect explained in 1905)
+ Diffraction observed in light so faint that photons seemed to have no mechanism to interact with each other (observed in 1909)
- A system similar to the one that led to the 1901 proposal that light energy is quantized as integral multiples of hf (except that Plank assumed that the walls were conductive.)
+ Photons striking metal and ejecting electrons (photo-electric effect explained in 1905)
- Diffraction observed in light so faint that photons seemed to have no mechanism to interact with each other (observed in 1909)
- A system similar to the one that led to the 1901 proposal that light energy is quantized as integral multiples of hf (except that Plank assumed that the walls were conductive.)
- The transfer of energy and momentum of a high energy photon of a nearly free electron.
$ Students will likely memorize only one aspect of this answer. I put the most important first (physical process), and expect other questions on other quizzes to reinforce that it is called the photo-electric effect.
