Ametal foil has a threshold frequency of 5.45× 1014 hz. which of the colors of visible light have enough energy to eject electrons from this metal?

a. red
b. orange
c. yellow
d. green
e. blue
f. indigo
g. violet

The colors of visible light that have enough energy to eject electrons from this metal?

         g. Violet          

          f. Indigo        

         e. Blue (Cyan)  

         d. Green           

Explanation:

1) Visible light frequency spectrum:

You need to look for the spectrum of frequencis of the visible light in a textbook or internet.

This is such spectrum:

Violet        680–790 THz  

indigo       620–680 THz  

Cyan        600–620 THz  

Green      530–600 THz  

Yellow      510–530 THz  

Orange     480–510 THz  

Red           405–480 THz  

2) Photoelectric effect

The photoelectric effect is the emission of electrons from a metal surface when a ray of light of enough energy shines on the surface of the metal.

The energy of ligth is directly related to the frequency, as the Planck - Einsen's equation shows:

Where

3) If the frequency of the ligth is below the threshold frequency of the metal, the electrons will not be emited.

Taking into account that 1 T unit =  10¹² units, 5.45 × 10¹⁴ Hz = 545 × 10¹² Hz = 545 THz, the coiors with frequency below 545 THz will not eject electrons from this metal.

These are the color which does have enough energy to eject electrons from this metal:

g. Violet                 680–790 THz  

f. Indigo                  620–680 THz  

e. Blue (Cyan)        600–620 THz  

d. Green                 530–600 THz  

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