The Total solution for NCERT class 6-12
Ultraviolet light of wavelength 2271 ├Е froma 100 W mercury source irradiates a photo-cell made of molybdenum metal. If thestopping potential is тИТ1.3 V, estimate the work function of the metal. Howwould the photo-cell respond to a high intensity (тИ╝105┬аW mтИТ2) redlight of wavelength 6328 ├Е produced by a He-Ne laser?
Wavelength of ultraviolet light,┬а╬╗┬а=2271 ├Е = 2271 ├Ч 10тИТ10┬аm
Stopping potential of the metal,┬аV0┬а=1.3 V
PlanckтАЩs constant,┬аh┬а= 6.6├Ч 10тИТ34┬аJ
Charge on an electron,┬аe┬а=1.6 ├Ч 10тИТ19┬аC
Frequency of light =┬а╬╜
We have the photo-energyrelation from the photoelectric effect as:
┬а=┬аh╬╜┬атИТ┬аeV0
Let┬а╬╜0┬аbe thethreshold frequency of the metal.
тИ┤=┬аh╬╜0
Wavelength of red light,┬а┬а= 6328 ├Ч 10тИТ10┬аm
Since┬а╬╜0>┬а╬╜r,the photocell will not respond to the red light produced by the laser.