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```									                                   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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