Ms.Burns+is+absent

Discussion Questions about Video: 10.French Physicist Louis de Broglie questioned, “If light exhibits dual wave-particle behavior, why can’t any particle of matter, such as an electron, exhibit a wave nature?” 11.The Heisenberg Uncertainty Principle reflects the wave-particle duality of light and matter: The more we know about matter as a particle (well-defined position), the less we know about its momentum (wavelength) and vice versa. 12.What did each of these scientists contribute to Quantum Physics? 13.How does a solar-powered calculator work? The light energy is taken by the mini solar panel, which converts the energy from light frequency to charge the battery and create voltage to keep the calculator working. 14.How does your cell phone’s digital camera work? When the picture is taken, the photons hit different panels at different frequencies and intensities, which can be digitally formed into an image. 15.How does a laser work? Lasers release photons to only hit a certain number of electrons, usually through a beam of light. 16. How do solar panels work? Solar panels convert energy obtained from photons (frequency) to electricity that can be used for household and office appliances.
 * 1) Upon what physical quantity does the color of any glowing body depend?
 * 2) Temperature.
 * 3) As the cells in a flashlight get weaker, the filament appears redder. Why?
 * 4) There is more frequency, so there will be less energy, which creates a smaller temperature than before.  There is a weaker current battery, so there is less energy, which means the filament will not reach as high of a temperature,and finally has lower frequency.
 * 5) The surface temperatures of Vega, our Sun, and Barnard’s star are 10,000 K, 6,000 K, and 3,000 K respectively. Which of these appears blue in color; red in color; yellow in color? Why?
 * 6) Vega is blue, the sun is yellow, and Barnard is red. This is all associated with their colors. Because frequency and temperature are directly related.
 * 7) What is the photoelectric effect?
 * 8) Electrons are emitted after they receive a certain level of energy. Which is caused by a photon of light and this certain level of energy is determined by a work function, so in order to create some kinetic energy for the electron to leave, there needs to be a higher frequency.
 * 9) As a mechanical analog of the photoelectric effect, consider a ball at rest in a depression. If a sufficient amount of energy, E, is given to the ball of mass, m, by the push of the hand, it will roll up the hill and escape with velocity v. Write an equation of energy conservation for this situation and explain each term in the equation by analogy to Einstein’s photoelectric effect equation.
 * 10) W(hand)=KE + GPE --> The ball is the electron, and once it receives a certain level of energy (hf), it has a velocity (KE in both instances). When the energy/work is big enough in both cases, it will be able to get to the top of the hill (GPE or the work function in terms of the photoelectric effect).
 * 11) An ultraviolet light discharges a negatively charged electroscope.
 * 12) The effect is known as **photoelectric**.
 * 13) Why isn’t the effect noticed when a glass plate is inserted between the zinc plate and the UV light? **Glass absorbs the UV light. Glass actually blocks it and allows visible light through **
 * 14) What does the work function usually denoted by **// Ψ //** represent?
 * 15) The amount of energy an electron needs to escape using the photoelectric effect.
 * 16) Rewatch the video at about the 7 minute mark. The upper half of the screen shows an electron trying to escape from the surface of the metal. The bottom half is a graph. The vertical axis represents the electric potential energy of the electron. As you watch the video, notice that the electron slides along the bottom line and slips up the edge to the bottom of the work function line. This represents the most energetic electrons, the ones that will escape from the surface if photons strike the surface with energy equal to or greater than the work function. If an electron absorbs a photon of ultraviolet light with energy **//hf//** greater than **// Ψ //**, what will happen to the electron?
 * 17) It will have kinetic energy and will then leave the metal.
 * 18) Use the table of work functions of various metals on page 1.
 * 19) If green light will cause the photoelectric effect to occur in sodium metal, for which other metals listed will it definitely also eject photoelectrons?
 * 20) Cesium and Potassium.
 * 21) What would be the effect of doubling the intensity of the light used?
 * 22) Energy stays same but number of photon doubles.
 * 23) What would be the effect of changing the color of the light used, for example, from green to blue or ultraviolet?
 * 24) Energy would change depending on frequency in a related matter.
 * 1) How did de Broglie relate a particle’s momentum to its wavelength?
 * 2) Through algebra manipulation, he proved that wavelength was equal to planck's constant divided by its momentum which is visible for particles that have very small mass.
 * 3) In the de Broglie model of the atom, if electrons are viewed as waves circling the nucleus, why do they have to exist in orbits that increase a whole wavelength at a time?
 * 4) The outer levels need to have less energy. Because frequency is inversely related to wavelength, the shorter wavelengths, near the nucleus will have higher frequencies, and thus have more energy (E=hf). Also, as waves they can only have whole wavelengths.
 * 5) Waves produce an interference pattern. How can the pattern be explained in terms of particle of light ?
 * 6) There will be bright sports of light in constructive interference.
 * 7) To what do the white light spots correspond where the wave pattern hits the screen?
 * 8) Constructive interference.
 * 1) How can a particle’s location be made more definite?
 * 2) Have momentum be really close to zero. Actually by adding waves of different wavelengths
 * 3) As the position of the wave becomes more definite, what happens to the momentum?
 * 4) Approaches zero.
 * 1) Planck- "Fathered" Quantum/Modern Physics through his planck's constant which detailed relation to energy and frequency of light being related.
 * 2) Einstein- Proved how planck's constant related to energy. Also came up with the notion of a work function and how it related to the energy. Instrumental in determining wave-particle duality, which revolutionized how light was viewed, especially the idea of photons. Completely revolutionized science.
 * 3) De Broglie- Came up with new model of atom to show electrons as waves and particles. Showed how wavelength had momentum. Set basis of wave mechanics.
 * 4) Schrodinger- His equation helped prove wave-particle duality. Expounded on De Broglie's wavelength equation.
 * 5) Heisenberg- Came up with the uncertainty principle.

OK... Got it. ~EB

Part 2

> A. Increasing the intensity of the light beam > B. Decreasing the intensity of the light beam > C. Increasing the wavelength of light > **D. Decreasing the wavelength of light** > **E. Increasing the frequency of light** > F. Decreasing the frequency of light > **G. Increasing the voltage of the battery** > H. Decreasing the voltage of the battery > I. Replacing the target with a material that has a larger work function > **J. Replacing the target with a material that has a smaller work function**
 * 1) Suppose you set up the experiment so that the plate is ejecting electrons. Predict which of the following changes to the experiment could increase the maximum initial kinetic energy of the ejected electrons. (Select all that apply) Then test your prediction.

> A. Increasing the intensity of the light beam > B. Decreasing the intensity of the light beam > C. Increasing the wavelength of light > **D. Decreasing the wavelength of light** > **E. Increasing the frequency of light** > F. Decreasing the frequency of light > G. Increasing the voltage of the battery > H. Decreasing the voltage of the battery > I. Replacing the target with a material that has a larger work function > **J. Replacing the target with a material that has a smaller work function**
 * 1) Suppose now you set up the experiment so that the light intensity is non-zero but the plate is NOT ejecting electrons. Predict which of the following changes to the experiment could make the plate start ejecting electrons? (Select all that apply) Then test your prediction.

> A. The force exerted on the electrons by the battery > **B. The beam of light shining on the plate** > C. Both A and B. > D. Neither A nor B.
 * 1) What causes the electrons to be ejected from the left plate in this simulation?


 * 1) Light is shining on a metal and electrons are being emitted. You turn the intensity down very very low. What do you observe? What conclusions can you draw about light, and why? how it is or is not consistent with what you would expect to observe if light matched the classical wave model and with what you would expect to observe if it matched the photon model of light.
 * 2) The lower the intensity, the fewer electrons that are emitted. I can conclude that the energy emitted also stems from the wavelength of the light. This throws a wrench in the classical wave model as waves were not believed to have mechanic qualities. However, this supports the photon model of light as the wavelength had momentum and carries a level of energy. Classical one also states intensity would have a factor, while photon model refers to KE for electrons leaving.


 * 1) Light is shining on a metal plate and electrons are being emitted. Without changing the intensity, you make the wavelength longer and longer. What do you observe? What conclusions can you draw about light, and why? how it is or is not consistent with what you would expect to observe if light matched the classical wave model and with what you would expect to observe if it matched the photon model of light.
 * 2) Less electrons are being emitted. This shows wavelength is inversely related to momentum, so frequency is directly related to it. Again, this is not consistent with the classic wave model as this shows wavelength having a direct (inverse) relationship with momentum. Therefore, it supports the photon model of light as the wavelength provides energy and momentum to the electrons. Wrong, same amount of electrons, only with more KE. Also classic model would say frequency would just prolong inevitable movement of electrons.


 * 1) In the photoelectric effect experiment, the graph of current vs battery voltage for a metal with light of a particular frequency shining on it looks like the curve below. This graph represents **current vs voltage** for **200nm light** shining onto **Cadmium (Cd)** which has **a work function of 4.07 eV**.

a) Explain your reasoning for __why__ this curve has the shape that it does. In your answer, you should address: Why is current level at V>0, why does current go to zero at some negative voltage and what determines that voltage, and why does current start decreasing steadily at V<0? At V>0, the electrons flow directly to the positive plate, as the experiment is set up so that the light is hitting the negative plate. Therefore, they naturally want to go to positive plate, and they have an extra energy to do so from the light. Because the __orientation__ of the plates, not __magnitude__, matters, there is a constant value for the setup as electrons flowed at same rate. When V<0, the electrons are excited by the light and thus flow away from the positive plate, which has the light shining on it now, but many are still attracted to the positive plate, so the current is reliant on the pressure difference of the plates. At a certain point, the positive plate simply becomes too much, so no electrons are able to flow to the other side as they are too attracted to the positive plate.

b) What is the stopping potential in this situation (in eV)? (Remember stopping voltage is expressed as a positive number). 4 eV (derived from 4 V when current is equal to 0). Wrong! eVs=KE=hf-(workfunction)  eVs =(6.626E-34*3E8 )/(1.6E-19*200E-9)-4.07= 2.17 eV

c) In the graphs below, the gray curve is always the same and represents the situation you explained in part a (the current vs voltage for 200nm light shining onto Cadmium (Cd) which has a work function of 4.07 eV). The red curves now represent the current vs voltage after a change in the experiment. Use the graphs to answer the questions that follow.

i) If you decrease the wavelength of the light shining onto the metal, what happens to the voltage where the current goes to zero...

**becomes a larger, negative number**

becomes a smaller, negative number

is unchanged

ii) Which graph would represent an increase in the intensity? E iii) Which graph would represent an increase in wavelength to 290nm? D C iv) Which graph would represent an increase in wavelength to 500 nm? G I  v) Which graph would represent a switch to sodium? I G vi) What change or combination of changes would you need to explain the change observed in Graph H above? (check all that apply)

**decrease in wavelength**

increase in wavelength

decrease in intensity

**increase in intensity**


 * 1) If you have the experiment set up so that electrons are being emitted from the metal plate, which of the following are true and which are false?
 * 2) As long as conditions do not change, all emitted electrons have the same initial kinetic energy. **True.**
 * 3) The work function for the metal is different for different electrons. **False. True **
 * 4) The energy of the photons hitting the plate must be less than the work function of the metal. **False.**
 * 5) The electrons emitted with the largest initial kinetic energy are those that were the least tightly bound in the metal **False (those close with metal will have shortest wavelength and highest frequency)**

444nm, as shown by this picture. This is the highest voltage where current is zero. eVs=KEmax = hf-(workfunction) e(0.5) =(6.626E-34 * 3E8 )/(1.6E-19 *λ)- 4.07 2.8 = 1.24E-6/λ 4.437E-7 m = λ
 * 1) You have a colored spot light, but you don't know its precise wavelength. To find out the wavelength you shine your light on a sodium target placed in a circuit as shown in the simulation. You look up the work function of sodium and find that it is 2.3 eV. If you set the battery voltage to -0.5 V, you find that the most energetic electrons nearly reach the right plate, but turn around just before they get there. What is the wavelength, in nm, of the colored light that you used? (You can answer this question either by doing a calculation or by using the simulation. To get practice for answering the next question, we recommend that you use both methods and check that they give the same answer.) SHOW YOUR WORK/EVIDENCE.

eVs=KEmax = hf-(workfunction) e(0.45) =(6.626E-34 * 3E8 )/(1.6E-19 *299E-9)-(workfunction) e(0.45) = 4.155-(workfunction) 3.7 eV 2. What is the mystery material? Magnesium
 * 1) You have a plate of metal, but you have no idea what kind of metal it is. You come up with the brilliant idea of measuring the work function of this metal by using it as the target in a photoelectric effect experiment. You can perform this experiment virtually by selecting '???' as the target in the simulation. SHOW YOUR WORK/EVIDENCE.
 * 2) What is the work function, in eV, of the mystery metal?

Note the "SHOW YOUR WORK" in all caps for numbers 8 and 9???? That means you need to show your work... equations, numbers plugged in, etc.


 * 1) The line on the graph of current to intensity can be described as **Linear**_
 * 2) The line on the graph of energy to frequency can be described as _**Linear**
 * 3) At a __frequency below__ the frequency required to overcome the work function, increasing the light intensity causes the current to //increase / decrease / **remain the same.**//
 * 4) At a __frequency above__ the frequency required to overcome the work function, increasing the light intensity causes the current to //**increase** / decrease / remain the same.//
 * 5) Old darkrooms (for developing film) were once illuminated with a feint red light (765nm). If this was the limit of the silver compound used in the film, solve for the work function of the silver compound. ___**1.62** eV____J__
 * Consider the following scenario: On a partly cloudy day you find that a household photovoltaic array outputs 2.4 amps of current. If the clouds part and the sun comes out, exactly doubling the amount of light incident on the PV array, we should expect the array to output //2.4 A / 4.8 A / more than 4.8 A / less than 2.4 A / **between 2.4 and 4.8 A**//**.**


 * 1) __ The work function for cesium is 1.96 eV. Find the cutoff wavelength for the metal. __ **633 n****m**
 * 2) **KE=0=hf-(work function)**
 * 3) **6.63E-34*f=1.96*1.6E-19**
 * 4) **f=6.34E14**
 * 5) **1/f=6.33E-7 m**
 * 6) What is the maximum kinetic energy for the emitted electrons when 425 nm light is incident on #7’s metal? **1.54****E-19** J
 * 7) **KE=hf-(work function)**
 * 8) **KE=6.63E-34*(1/4.25E-7)-(1.96*1.6E-19)**
 * 9) **KE=1.54 J**
 * 10) In certain metal, the stopping potential is found to be 3.70 V. When 235 nm light is incident on the metal, electrons are emitted. What is the maximum kinetic energy given to the electrons in eV and J? ___ **.99** eV__ **1.58E****-19** J
 * 11) **KE=hf-(work function)**
 * 12) **3.7*1.6E-19=6.63E-34/(4.25E-7)-(workfunction)**
 * 13) **work function= 1.24E-19J**
 * 14) **KE=6.63E-34/(2.35E-7)-1.24E-19**
 * 15) **KE= 1.58E-19J**

10.Stars vary in color. Which color indicates the hottest surface temperature of a star?


 * 1) Red
 * 2) Orange
 * 3) Yellow
 * 4) **Blue**

11.Which of the following ojbects, all moving at the same speed, would have a de Broglie wavelength associated with them that would be larger than that of a proton travelling a the same speed?


 * 1) **An electron**
 * 2) A neutron
 * 3) A bacteria
 * 4) A baseball

12.When green light shines upon a given metal, it emits phtoelectrons. Which of the following will also produce photoelectric emission, using this same metal?


 * 1) **Low intensity blue light**
 * 2) Low intensity red light
 * 3) High intensity red light
 * 4) high intensity yellow light

13.Ultraviolet light shines upon a sheet of zinc metal, and photoelectrons are emitted. If the intensity of the light is increased,


 * 1) The electrons will have less energy.
 * 2) The electrons will have more energy
 * 3) **More electrons will be emitted**
 * 4) Fewer electrons will be emitted.

14.Consider the following frequencies of electromagnetic radiation. Which photon has the greatest energy?


 * 1) 6.6 x 10-34 Hz
 * 2) 6.6 x 10-4 Hz
 * 3) 6.6 x 104 Hz
 * 4) **6.6 x 1018 Hz**

15.Compared to a photon of blue light, a photon of red light has


 * 1) More energy
 * 2) Less energy
 * 3) Shorter wavelength
 * 4) **The same wavelength**

16.An electron is confined to a box of sides L and it has a definite speed. If the walls of the box were to move inward so that the box shrinks, the electron


 * 1) Would speed up
 * 2) Would slow down
 * 3) **Would move with the same speed**
 * 4) Would exhibit none of the above.

17.The idea of packets or quanta of energy originated with


 * 1) Louis de Broglie
 * 2) **Max Planck**
 * 3) Werner Heisenberg
 * 4) Erwin Schrodinger

18.A matter wave


 * 1) Applies only to “massless” particles
 * 2) Applies only to a photon
 * 3) **Has a wavelength inversely related to its momentum**
 * 4) Has a wavelength directly related to its momentum

19.Which of the following does not demonstrate the wave nature of matter?


 * 1) **The cloud model of the electron**
 * 2) The two slit interference pattern
 * 3) An electron in motion in a conducting wire (circuits)
 * 4) Electron diffraction

20.When doing the photoelectric effect experiment,


 * 1) What determines the amount of kinetic energy photoelectrons will have? **The frequency/wavelength and work function of the metal.**
 * 2) What determines the number of photoelectrons emitted from a metal? **Intensity of the light.**