In: Chemistry
Light from three different lasers (A, B, and C), each with a different wavelength, was shined on the same metal surface. Laser A produced no photoelectrons. Lasers B and C both produced photoelectrons, but those produced by B had a greater velocity than those produced by C. Arrange the lasers in order of increasing wavelength.
If A didn't produce any photoelectrons, Wouldn't it just be a straight line with the highest frequency? And to have a greater velocity would that mean the wavelength increases frequency?
This problem is based on photoelectric effect.
Each metal has different work function. It is nothing but the energy required to remove the electron from the surface .Equation is
K.E is kinetic energy of electron.
When Q is large energy needed by photon is large and vice versa.
When incoming photon has enough energy to remove an electron from metal surface, electron is ejected.
If the energy insufficient to remove an electron or is less than its work function then electron is not removed.
Here light from laser A could not remove an electron from metal surface. This means that energy of photon is less than work function Q.
Both C and B could remove an electron from the surface of metal.
After removing electrons rest energy of photon is transferred to ejected electron and this energy is converted to kinetic energy.
By all of this argument we can say that
Energy of B is highest and then it is followed by C . A has lowest energy among all.
Lets write the trend in energy from lowest to highest
A<C<B
We know,
The relation between energy and wavelength
The relation is :
This equation shows that energy is inversely proportional to the wavelength.
So the trend in wavelength is opposite to the energy. Lets show it.
Increasing wavelength.
B<C<A