Photoelectric Effect (1 Viewer)

[sikeveo]

A physics student was conduction an investigation on the photelectric effect. The student used an infrared laser with a wavelength of 1.55 x 10^-6 m for this investigation. Please note that it is ten to the minus 6.

(b) When the laser light was shone onto a photo cell, no current was detected. The student increased the intensity of the light but still detected no current. Explain this observation.

Can someone help please? My teacher is crap ><

 

[Dumsum]

Infrared is well below the general "threshold frequency" for which the photons will have enough energy to 'boil off' electrons.

Threshold frequency - the frequency of light which when shone on a certain metal will cause electrons to be emitted from the surface of the metal.

You say photo cell, I assume this means like solar cells, we weren't taught it directly but I think I'd be correct in assuming the same sort of thing would apply to silicon before electrons could enter the conduction band.

Anyone feel free to correct me

 

[nanashi]

yeh thats right
the higher the frequency, the higher the energy. infrared does not have enough energy to make the electrons be emitted from the surface of the cell.
increasing the intensity wouldnt do anything (coz its infrared). But if it was ultraviolet light, and electrons were being emitted, increasing the intensity would increase the number of photons hitting the surface, so there would be more electrons being emitted.

 

[sikeveo]

i see, so you'd probably need UV or something similar to enable the current to flow and be detected

 

[nanashi]

yeh
infrared does not have enough energy to make the electrons move to the conduction band. so no current would be detected

 

[rama_v]

You would also have to state Planck's formula E=hf because it is this formula that shows why light of higher frequency has higher energy photons.

 

[nanashi]

oh yeh.. forgot about that