Photoelectric Effect 1) When light falls on a metal, the stopping potential that stops the emitted photoelectrons is -3.5 V. a) What is the maximum kinetic energy given to electrons by the incident light? State your answer in J and eV. [5.6 x 10-19 J, 3.5 eV] b) What is the speed of the electrons? [1.1 x 106 m/s] 2) The maximum kinetic energy, for a metal, given to electrons from incident light is 4.5 eV. What is the stopping potential? [-4.5 V] 3) A certain metal has a threshold frequency of 1.5 x 1014 Hz. a) What is the work function in J and eV? [9.9 x 10-20 J, 0.62 eV] b) The metal is irradiated by 300. nm light. What is the maximum kinetic energy of the photoelectrons in eV? [3.5 eV] 4) Light shines on a metal photocell which has a binding energy of 1.40 eV. The energy of the most energetic electrons is 0.89 eV. What is the wavelength of the light? [5.4 x 10-7 m] 5) The stopping potential of photoelectrons is -5.3 V. What is the maximum kinetic energy of the electrons? [8.5 x 10-19 J] 6) The work function of a metal is 6.4 eV. What is the threshold frequency? [1.5 x 1015 Hz] 7) A metal has a threshold frequency of 3.3 x 1014 Hz. You shine light with a frequency of 2.0 x 1015 Hz on the metal. Calculate the max kinetic energy of the photoelectrons. [1.1 x 10-18 J] 8) A certain metal has a work function of 2.63 eV. Find the lowest frequency of light that will just liberate an electron. [6.35 x 1014 Hz] 9) Sodium metal has a threshold wavelength of 540. nm. a) Find the binding energy of an electron of sodium. [3.68 x 10-19 J] b) What is the max Ek, in eV, of a photoelectron emitted from this surface when light of 200. nm shines on it? [3.91 eV] 10) The max Ek of electrons emitted from a metal is 1.6 x 10 -19 J when the incident radiation is 7.5 x 1014 Hz. What is the minimum frequency of radiation for which electrons will be emitted? [5.1 x 1014 Hz] 11) The stopping potential to prevent electrons from flowing across a photoelectric cell is -4.0 V. Find the max Ek of electrons emitted in J and eV. [6.4 x 10-19 J, 4.0 eV] 12) Light of 500 nm illuminates a metal surface. What voltage is needed to stop all the photoelectrons emitted if the binding energy is 2.0 eV? [0.49 V] 13) How does the photoelectric effect demonstrate the particle nature of light? 14) The threshold frequency of tin is 1.1 x 1015 Hz. a) What is the work function of tin? [7.3 x 10-19 J] b) If light of 1.8 x 1015 Hz falls on tin, what is the max Ek of the emitted electrons? [4.6 x 10-19 J] 15) Use the following graph to answer this question: 5 6 Ek (max) 10-19 J 4 3 2 1 Frequency 1014 Hz 1 2 3 4 5 6 7 8 9 10 12 a) Find the value of Planck’s constant from this graph. [~7.5 x 10-34 J/Hz] b) What is the threshold frequency of this metal? [4.0 x 1014 Hz] c) What is the threshold wavelength of this metal? [7.5 x 10-7 m] d) Will the photoelectric effect occur if the threshold wavelength is exceeded? Why? e) What is the work function of this metal? [3.0 x 10-19 J] f) What would be an alternate method of finding the binding energy? 16) What would be the difference if red or violet light were used in a photoelectric effect experiment, on a metal sensitive to the entire visible spectrum? 17) What wavelength of EMR will cause photoelectrons to be knocked loose from a tungsten surface (W = 4.53 eV), if the emitted photoelectrons have a max speed of 0.10 c? [4.8 x 10-10 m] 18) The work function for a metal is 2.0 x 10-19 J. What would be the stopping voltage if light of 500. nm shines on the metal? [-1.2 V] 19) What voltage would stop photoelectrons emitted by a metal surface, which requires a threshold frequency of 6.0 x 1014 Hz, if 300. nm light shines on the metal? [-1.7 V] 20) The work function of sodium is 2.3 eV. What is the longest wavelength that can cause photoelectric emission? [5.4 x 10-7 m] 21) Will photoelectrons be emitted by a copper surface (W = 4.4 eV) when illuminated by visible light? [No, needs 283 nm to produce effect] 22) The work function for a metal is 2.0 x 10-19 J. What is the threshold frequency and the stopping voltage for 500.nm light? [3.0 x 1014 Hz, -1.2 V] 23) Barium has a work function of 2.48 eV. a) What is the max Ek of ejected electrons if 450. nm light shines on it? [4.52 x 10 -20 J] b) What is their max speed? [3.15 x 105 m/s] c) What cut-off potential would stop these electrons? [-0.283 V] 24) A photoelectron has Ek = 3.4 eV. What incident wavelength to 4 sig digs shines on the metal surface if fo = 1.5 x 1014 Hz? [3.091 x 10-7 m] 25) Explain the following terms: threshold frequency, photoelectron, photoelectric effect, binding energy, photoelectric effect, quantum, photoelectric current.
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