6) Photoelectric Effect and Uncertainity Problems

1. Calculate the work function of sodium if its threshold wavelength is 5040 Å.
2. The work function of sodium is 2.46 eV and its threshold wavelength is 5040 Å, calculate the
planks constant.
3. The maximum energy of an electron emitted from the photoelectric surface of work function
2.2 eV illuminated by monochromatic radiation is 0.8 eV. What is the wavelength of the light
incident on the surface.
4. What is the threshold wavelength of a Nickle whose work function is 4.84 eV.
5. A photon of wavelength 3310 Å falls on a photo cathode and ejects an electron of maximum
energy 3x10-19 joule. Calculate the work function of the cathode material.
6. A work function of potassium surface is 2.2 eV, when U-V light of wavelength 3200 Å falls on
the surface, calculate the energy of the most energetic photon emitted. What is the
threshold frequency of potassium.
7. Work function of sodium is 2.3 eV. Does sodium show photoelectric effect with orange light
with wavelength 6800 Å. What will be the maximum Kinetic energy of the photo electron, if
2000 Å light falls on the sodium surface.
8. Find out the maximum energy of photoelectron, work function and threshold frequency,
when a light of wavelength 313 nm is incident on the surface of the cesium and the stopping
potential for the photo electron is 1.98 V.
9. A proton and a photon both have kinetic energy equal to 5 keV. Are their de-Broglie
wavelengths equal? If not, estimate their de-Broglie wavelengths?
10. The threshold frequency for photo electric emission in copper is 1.1x1015 sec-1. Find the
maximum energy of photoelectrons when light of frequency 1.5x1015 sec-1 falls on copper
surface. Also calculate the retarding potential.
11. The work function of sodium is 2.27 eV. What is the velocity of the electrons emitted by light
of wavelength 4000 Å.
12. UV light of wavelength 800 Å and 700 Å when allowed to fall on a certain metal is found to
liberate electrons with kinetic energy of1.8 eV and 4 eV respectively. Find the planks
constant.
13. In an experiment tungsten cathode which has a threshold 2300 Å is irradiated by UV light of
wavelength 1800 Å. Calculate maximum energy of emitted photo electron and work
function of tungsten.
14. Electrons are emitted with zero velocity from a certain metal surface when it is exposed to
the radiation of wavelength 6800 Å. Calculate the threshold frequency and work function of
metal.
15. Calculate the stopping potential for the photoelectrons emitted by gold cathode if the
wavelength of the incident radiation is 2x10-7 m. Given the work function of gold is 4.80 eV.
16. What potential difference should be applied to stop the fastest photoelectrons emitted by
nickel surface under the action of 20 nm UV light? The work function of nickel is 5.01 eV.
17. Light of wavelength 5893 Å is incident on a potassium surface. The stopping potential for the
emitted electrons is 0.36 V. Calculate the maximum energy of photoelectrons, work function
and threshold frequency.
18. Calculate the maximum velocity of the electrons ejected from the metal surface having work
function 5 eV by an incident radiation of 161 nm.
19. Calculate the velocity of photo-electron, if the work function of the target material is 1.24 eV
and the wavelength of incident light is 4.36x10-7 m. What retarding potential is necessary to
stop the emission of these electrons?
20. If photo-electric emission from a given target velocity of emitted electron is 1x106 m/sec.
When the light of wavelength 2.5x10-7 m is used. Calculate the velocity of emitted electrons
with light of wavelength 5x10-7 m and also calculate the work function of the target in eV.
21. If the uncertainty in position of an electron is 4x10-10 m, calculate the uncertainty in

momentum.
22. An electron has a speed of 600 m/s with an accuracy of 0.005 %. Calculate the uncertainty
with which we can locate the position of the electron.
23. Show if the uncertainty in the location of a particle is equals to its de-Broglie wavelength,
the uncertainty in its velocity is equal to its velocity.
24. A microscope using photons is employed to locate an electron in an atom to within a

distance of 0.1 Å. What is the uncertainty in the momentum of electron located in this way?
What is the uncertainty in velocity.
25. Compare the uncertainties in the velocities of an electron and a proton confined to 1nm box.
26. Calculate the smallest possible uncertainty in the position of an electron moving with a
velocity 3x107 m/sec.
27. An electron is confined to a box of length 10-9 m. Calculate the minimum uncertainty in its
velocity.
28. Using uncertainty relation ∆E. ∆t=h/4π calculate the time required for atomic system to
retain the excitation energy for a line of wavelength 6000 Å and width 10-4 Å.
29. An electron has a speed of 3.5x107 cm/sec accurated to 0.0098%. with what fundamental
accuracy can we locate the position of electron.
30. Assume that an electron is inside a nucleus of radius 10-15 m. Using uncertainty principle,
estimate the kinetic energy of the electron in eV.
31. How does the concept of Bohr’s orbit violates the uncertainty relation. Explain
32. The position and momentum of a 1 keV electron are simultaneously measured. If the
position is located within 1 Å. What is the percentage of uncertainty in momentum.
33. The uncertainty in the location of a particle is equal to its De-Broglie wavelength. Calculate
the uncertainty in its velocity.
34. Wavelengths can be determined with accuracies of one part in 106. What is the uncertainty
in the position of a 1 Å X-ray photon when its wavelength is simultaneously measured?

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1. Calculate the work function of sodium if its threshold wavelength is 5040 Å.

21. If the uncertainty in position of an electron is 4x10-10 m, calculate the uncertainty in

24. A microscope using photons is employed to locate an electron in an atom to within a

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