A.P. Physics 2 Modern Physics Practice Test

Transcription

1 A.P. Physics 2 Modern Physics Practice Test Name: Figure 1: Diagram of the energy levels for the hydrogen atom. 1. Determine the frequency of light emitted when an electron jumps down from the third energy level to the ground state level. Determine the wavelength of light emitted and the type of radiation as well. 2. Determine if hydrogen in its ground state is transparent to light that is incident upon it of wavelength of 122 nm. Figure 2: A piece of silver that has a work function of 4.64 ev. 1. Determine the threshold frequency for silver. 2. If light of 193 nm is incident upon the silver in Figure 2, determine the kinetic energy maximum for the electrons that are emitted.

2 Figure 3: Diagram of the de Broglie equation along with the variable interpretations. 1. Discuss examples of how an electron can be interpreted as a wave and as a particle. 2. Use Einstein s equations for a wave (c = ) and Plank s equation (E = h ) to derive the de Broglie equation. 3. Describe the nature of all particles using the de Broglie equation in terms of when objects are in motion and when the de Broglie wavelength becomes significant for the particle. 4. How are atoms described today in terms of quantum mechanics? Mention ideas from Plank, Max Born, Neils Bohr, Schrodinger, Heisenberg, and energy level diagrams.

3 Figure 4 Diagram of an LED placed into a circuit in order to measure the potential difference when the LED begins to glow. LED Color Wavelength (nm) Potential Difference (V) Violet Blue Green Yellow Orange Red Using your calculator, make a graph of the energy for the photons vs. frequency of the photons and use linear regression to estimate Plank s constant using the slope of the graph. Figure 5: Diagram of a photoelectric experiment that measures the stopping potential for electrons that are emitted.

4 1. Follow the link provided in the review site and download the Photoelectric Effect PHET Simulation. Then perform the experiment using sodium (work function = 2.28 ev). Change the wavelength of light several times and cause the electrons to stop just before the right plate each time by applying a negative voltage. Fill in the data chart below. Wavelength (nm) Stopping Potential (Volts) 2. Make an appropriate graph to calculate the work function, the cutoff frequency (threshold frequency) and Plank s constant. 3. Then answer the following questions: (a) How does the stopping potential relate to maximum electron kinetic energy? (b) Why do we emphasize that this is maximum kinetic energy and not just kinetic energy? (c) Why do we graph frequency and not wavelength? (d) What is the physical significance of the cut-off frequency? (e) What is the significance of the work function? (f) Do you expect all metals to exhibit the photoelectric effect? Why or why not? (f) What effect does increasing the intensity of light have on the experiment?

5 Figure 6: Diagram of a crystal that is being x-rayed in order to determine the spacing between the layers of atoms in the crystal. 1. Using the concepts of double slit diffraction, modify the equation for double slit diffraction in order to calculate the spacing between the layers of the atoms. 2. If electrons of wavelength (0.314 nm) is incident upon the surface of the crystal at an angle of causes a first order constructive interference pattern, determine the spacing between the layers of the atoms. Figure 7: Light that is unpolarized is incident upon a layer of glass (n=1.45). 1. Determine the angle of incidence that will allow the reflected light to be polarized. Figure 8: Light (I = 15 W/m 2 ) is vertically polarized at point a and is analyzed at point b. 1. Determine the intensity of light at the analyzer if the angle between the vertical and the analyzer is 30 0.

6 Nuclear Energy 1. Determine the nuclear binding energy ( E) and the binding energy per nucleon ( E/A) for Osmium-190. mass of 190 Os = amu mass of neutron = amu mass of proton = amu Figure 9: Binding energies for the elements on the periodic table. 1. Based on the graph in Figure 9, which element on the periodic table to expect to be the most stable element?

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