Photoelectric+Effect

= Part 1: 2/27/12 = toc > *Temperature > *The dim red light in the filament has the same amount of energy as the filament glowing a brighter red light. However, as seen in the equation E=hf, as the energy decreases so does the frequency, giving off a redder appearance because red is the lowest frequency visible light. > *Vega = Blue > *Sun = Yellow > *Barnard = Red >  *The photoelectric effect proves that energy is released in packages (quantum). When the substance (metal) is bombarded by photons, electrons will be released. Light can force electrons to be emitted. The electrons emitted have a definite minimum frequency. One photon is absorbed by each photoelectron that the metal ejects. When the energy of the light is greater than the work function, electrons will be emitted and there will be KE. >  *E = GPE + KE (E is the photon's energy, GPE is like the work function and KE is like the KE of the electron being emitted) 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? 14.How does your cell phone’s digital camera work? 15.How does a laser work? 16.How do solar panels work?
 * 1) Upon what physical quantity does the color of any glowing body depend?
 * 1) As the cells in a flashlight get weaker, the filament appears redder. Why?
 * 1) The weaker battery creates a smaller current. Because there is a smaller current, there is less energy so the filament's temperature is lower. The lower temperature means a lower frequency so the as the frequency decreases the filament gives off a redder appearance.
 * 2) 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? *The hottest object will appear blue, the middle one will appear yellow, and the lowest will appear red. As temperature decreases, frequency decreases.
 * 1) What is the photoelectric effect?
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">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.
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">An ultraviolet light discharges a negatively charged electroscope. What does the work function usually denoted by **// Ψ //** represent?
 * The effect is known as **the photoelectric effect**.
 * Why isn’t the effect noticed when a glass plate is inserted between the zinc plate and the UV light? *The glass will filter the UV light. This stops the photoelectrons from discharging. Visible light photons do not have enough energy to emit electrons from zinc.
 * 1) What does the work function represent?
 * An electron in a metal lacks enough energy to escape by an amount called the work function. (binding energy)
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">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? *The electron will escape from the metal.
 * 2) <span style="font-family: Arial,Helvetica,sans-serif;">Use the table of work functions of various metals on page 1.
 * If green light will cause the photoelectric effect to occur in sodium metal, for which other metals listed will it definitely also eject photoelectrons?
 * Potassium and Cesium
 * What would be the effect of doubling the intensity of the light used?
 * Number of photons doubles
 * Energy provided by each photon remains constant
 * What would be the effect of changing the color of the light used, for example, from green to blue or ultraviolet?
 * Changing the color of the light used changes the amount of energy provided.
 * Changing from green to blue would be providing more energy. KE will of photoelectrons increases.
 * <span style="font-family: Arial,Helvetica,sans-serif;">How did de Broglie relate a particle’s momentum to its wavelength?
 * [[image:Screen_shot_2012-02-27_at_10.57.48_PM.png width="322" height="223"]]
 * can see this with small masses
 * <span style="font-family: Arial,Helvetica,sans-serif;">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?
 * Electrons show properties of waves and particles. So, a half of a wavelength cannot exist. Also, orbitals can only exist in whole wavelengths. The crests and troughs of each wave must match up therefore constructive and destructive interference can take place.
 * <span style="font-family: Arial,Helvetica,sans-serif;">Waves produce an interference pattern. How can the pattern be explained in terms of particle of light ?
 * When a particles hit a surface, the create a spot of light.
 * This is also what occurs in wave interference.
 * <span style="font-family: Arial,Helvetica,sans-serif;">To what do the white light spots correspond where the wave pattern hits the screen?
 * Constructive interference
 * <span style="font-family: Arial,Helvetica,sans-serif;">How can a particle’s location be made more definite?
 * We need to be less certain about the particle's momentum.
 * Add different wavelengths
 * <span style="font-family: Arial,Helvetica,sans-serif;">As the position of the wave becomes more definite, what happens to the momentum?
 * The momentum of the wave becomes less certain.
 * <span style="font-family: Arial,Helvetica,sans-serif;">Planck:
 * <span style="font-family: Arial,Helvetica,sans-serif;">Discovered Planck's constant (relationship between energy of particles leaving in the photoelectric effect and the frequency of the light that hit them)
 * <span style="font-family: Arial,Helvetica,sans-serif;">quanta (packages of light)
 * <span style="font-family: Arial,Helvetica,sans-serif;">Einstein:
 * <span style="font-family: Arial,Helvetica,sans-serif;">Used the photoelectric effect to proved Planck's theory
 * <span style="font-family: Arial,Helvetica,sans-serif;">E=mc^2
 * <span style="font-family: Arial,Helvetica,sans-serif;">De Broglie:
 * Wave-particle duality of light and of all matter
 * p=h/wavelength
 * <span style="font-family: Arial,Helvetica,sans-serif;">Schrodinger:
 * <span style="font-family: Arial,Helvetica,sans-serif;">the energy of an electron is always that of a quantized energy level (electron cloud model)
 * <span style="font-family: Arial,Helvetica,sans-serif;">Heisenberg:
 * <span style="font-family: Arial,Helvetica,sans-serif;">Discovered the uncertainty principle
 * The light that hits the calculator causes the photovoltaic effect to occur. This process is similar to the photoelectric effect. This creates current within the calculator, allowing it to function.
 * Photons hit the camera's lens at different frequencies and intensities as the photograph is taken. The camera is able to interpret these frequencies and intensities in order to produce the image with the correct color pixels.
 * CCD and CMOS image censors convert light into electrons. Once the sensor converts the light into electrons it reads its accumulated charge of each cell in the image.
 * Laser stands for Light Amplification by Stimulated Emission of Radiation. Lasers generate a monochromatic beam of photons. Lasers stimulate the emission of photons by exciting a certain number of electrons.
 * The lasing medium is "pumped" to excite the atoms. The excited electrons emit energy (photons). The photon emitted has a specific wavelength that depends on the state of the electron's energy when it is released.
 * Light hits the solar panels. The photons' energy is absorbed, exciting electrons, and creating current and voltage. This provides energy. Made of special semiconductors (silicon).

OK... Got it. Some of these responses are perfunctory. I hope you know the details better than these explanations demonstrate. ~EB

=<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12pt;">Part 2: 2/28/12 =

> 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 > <span style="color: #0000ff; font-family: Arial,Helvetica,sans-serif;">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) <span style="font-family: Arial,Helvetica,sans-serif;">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.


 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">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. 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) <span style="font-family: Arial,Helvetica,sans-serif;">What causes the electrons to be ejected from the left plate in this simulation?
 * <span style="font-family: Arial,Helvetica,sans-serif;">A. The force exerted on the electrons by the battery
 * **<span style="font-family: Arial,Helvetica,sans-serif;">B. The beam of light shining on the plate **
 * <span style="font-family: Arial,Helvetica,sans-serif;">C. Both A and B.
 * <span style="font-family: Arial,Helvetica,sans-serif;">D. Neither A nor B.

>> <span style="font-family: Arial,Helvetica,sans-serif;">*Less electrons are emitted when the intensity is down very very low. >> <span style="font-family: Arial,Helvetica,sans-serif;">*Kinetic energy remains the same >> <span style="font-family: Arial,Helvetica,sans-serif;">*This shows that intensity effects the number of electrons emitted and NOT the kinetic energy. >> <span style="color: #0000ff; font-family: Arial,Helvetica,sans-serif;">*According to the classical wave model, increasing intensity would increase energy (more KE). (This shows how this matches the photon model of light and not the classical wave model.)
 * 1) <span style="color: #000000; font-family: Arial,Helvetica,sans-serif;">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.


 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">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.
 * Number of electrons emitted stays the same. KE increases. Increasing the wavelength (decreasing the frequency) increases the KE. Changing the wavelength (and frequency) does not change the number of electrons emitted. The classical wave model says that even low frequency light would provide enough energy over time to emit electrons.


 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">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**.
 * 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?
 * The current stays the same level at V>0 because positive voltage has no effect on the number of electrons emitted in the experiment.
 * Current goes to zero at some negative voltage because the electrons move back towards the plate when voltage is negative, decreasing current. This is also why current starts decreasing steadily at V<0. I=0 when V=stopping potential of the circuit.
 * What is the stopping potential in this situation (in eV)? (Remember stopping voltage is expressed as a positive number.)
 * eVs = KE = hf - work function
 * eVs = 6.626*10^-34 (3*10^8) - 4.07 = 2.17eV
 * 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.
 * 1) 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
 * <span style="font-family: Arial,Helvetica,sans-serif;">is unchanged
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">Which graph would represent an increase in the intensity?
 * E (intensity increases --> stopping potential remains the same)
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">Which graph would represent an increase in wavelength to 290nm?
 * C (wavelength increases --> stopping potential decreases & current decreases)
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">Which graph would represent an increase in wavelength to 500 nm?
 * I large wavelength --> current equals 0 --> frequency is below cutoff frequency --> no electrons ejected
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">Which graph would represent a switch to sodium?
 * G Sodium's eVs = 3.5 eV (little lower than Cadmium) --> eVs --> cutoff wavelength is higher for sodium --> current will be smaller at any given wavelength
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">What change or combination of changes would you need to explain the change observed in Graph H above? (check all that apply)
 * **<span style="font-family: Arial,Helvetica,sans-serif;">decrease in wavelength **
 * increase in wavelength
 * <span style="font-family: Arial,Helvetica,sans-serif;">decrease in intensity
 * **<span style="font-family: Arial,Helvetica,sans-serif;">increase in intensity **


 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">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.
 * False, all emitted electrons do not have the same initial KE.
 * 1) The work function for the metal is different for different electrons.
 * False, work function is a property of the metal.
 * 1) The energy of the photons hitting the plate must be less than the work function of the metal.
 * False, if the energy of the photons hitting the plate is less that the work function of the metal, the electron will absorb the photon without gaining enough energy to escape the metal plate.
 * 1) The electrons emitted with the largest initial kinetic energy are those that were the least tightly bound in the metal
 * True, the maximum kinetic energy results when the least tightly-bound electrons break free from the metal.

>> e(0.5) =(6.626*10^-34)(3*10^8 )/(1.6*10^-19 *wavelength)-4.07 >> wavelength = 4.437*10^-7m
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">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.
 * Wavelength =433nm
 * [[image:Screen_shot_2012-02-29_at_6.37.24_AM.png width="514" height="384"]]
 * eVs = KE = hf - work function


 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">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) <span style="font-family: Arial,Helvetica,sans-serif;">What is the work function, in eV, of the mystery metal?
 * eVs = KE = hf - work function
 * e(0.45) = 6.626*10^-34(3*10^8)(1.6*10^-19)(299*10^-9) - work function
 * work function = 3.7eV
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">What is the mystery material?
 * Magnesium (work function = 3.68 eV)

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.

=Part 3: 2/29/12=
 * 1) The line on the graph of current to intensity can be described as **linear (showing that current and intensity are directly proportional).**
 * 2) The line on the graph of energy to frequency can be described as **linear (the positive slope is equal to Planck's constant and the y-intercept is equal to the work function of the metal).**
 * 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. __3.92*10^14 eV__
 * c=f*wavelength
 * 3*10^8=f(765*10^-9)
 * frequency = 3.92*10^14 Hz
 * E=hf - work function
 * 0 = (6.63*10^-34)(3.92*10^14) - work function
 * work function = 2.6*10^-19 J *(6.24*10^18)
 * work function = 3.92*10^14 Hz
 * 1) 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//.
 * 2)  The work function for cesium is 1.96 eV. Find the cutoff wavelength for the metal. **__6.34*10^-7__** **__m__**
 * E = hf - wavelength
 * 0 = (6.63*10^-34)*f - (1.96) * (1.6*10^-19)
 * f = 4.73*10^14Hz
 * c = f*wavelength
 * 3*10^8 = (4.73*10^14) * wavelength
 * wavelength = 6.34*10^-7 m
 * 1) What is the maximum kinetic energy for the emitted electrons when 425 nm light is incident on #7’s metal? **__1.54*10^-19J__**
 * c = f * wavelength
 * 3*10^8 = f * (425*10^-9)
 * f = 7.06*10^14Hz
 * E = hf - work function
 * KEmax = (6.63*10^-34)*(7.06*10^14) - (1.96)*(1.60^-19)
 * KEmax = 1.54*10^-19J
 * 1) 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? **__2.15eV__**
 * c = f * wavelength
 * 3*10^8 = f * (425*10^-9)
 * f = 7.06*10^14Hz
 * E = hf - work function
 * (3.70)(1.6*10^-19) = (6.63*10^-19) * (7.06*10^14) - work function
 * work function = 1.24*10^-19 eV
 * E = hf - work function
 * KE max = (6.63*10^-34) (7.06*10^14) - (1.24*10^-19)
 * KE max = 3.44*10^-19 J (6.24*10^18)
 * KE max = 2.15 eV
 * 1) Stars vary in color. Which color indicates the hottest surface temperature of a star?
 * 2) Red
 * 3) Orange
 * 4) Yellow
 * 5) __** Blue **__
 * 6) 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?
 * 7) __** An electron **__
 * 8) A neutron
 * 9) A bacteria
 * 10) A baseball
 * 11) When green light shines upon a given metal, it emits phtoelectrons. Which of the following will also produce photoelectric emission, using this same metal?
 * 12) __**Low intensity blue light**__
 * 13) Low intensity red light
 * 14) High intensity red light
 * 15) high intensity yellow light
 * 16) Ultraviolet light shines upon a sheet of zinc metal, and photoelectrons are emitted. If the intensity of the light is increased,
 * 17) The electrons will have less energy.
 * 18) The electrons will have more energy
 * 19) __** More electrons will be emitted **__
 * 20) Fewer electrons will be emitted.
 * 21) Consider the following frequencies of electromagnetic radiation. Which photon has the greatest energy?
 * 22) 6.6 x 10-34 Hz
 * 23) 6.6 x 10-4 Hz
 * 24) 6.6 x 104 Hz
 * 25) __** 6.6 x 1018 Hz **__
 * 26) Compared to a photon of blue light, a photon of red light has
 * 27) More energy
 * 28) Less energy
 * 29) Shorter wavelength
 * 30) **__ The same wavelength __**
 * 31) 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
 * 32) Would speed up
 * 33) Would slow down
 * 34) **__ Would move with the same speed __**
 * 35) Would exhibit none of the above.
 * 36) The idea of packets or quanta of energy originated with
 * 37) Louis de Broglie
 * 38) **__ Max Planck __**
 * 39) Werner Heisenberg
 * 40) Erwin Schrodinger
 * 41) A matter wave
 * 42) Applies only to “massless” particles
 * 43) Applies only to a photon
 * 44) **__ Has a wavelength inversely related to its momentum __**
 * 45) Has a wavelength directly related to its momentum
 * 46) Which of the following does not demonstrate the wave nature of matter?
 * 47) __**The cloud model of the electron**__
 * 48) The two slit interference pattern
 * 49) An electron in motion in a conducting wire (circuits)
 * 50) Electron diffraction
 * 51) When doing the photoelectric effect experiment,
 * 52) What determines the amount of kinetic energy photoelectrons will have?
 * Wavelength
 * 1) What determines the number of photoelectrons emitted from a metal?
 * Intensity