Question

What is the threshold frequency for sodium metal if a photon with frequency 6.66 x 10^14 sâ1 ejects an electron with 7.74 x 10^â20 J kinetic energy? Will the photoelectric effect be observed if sodium is exposed to orange light?

Answer 1

Answer: The threshold frequency of sodium metal is
`5.49* 10^(14)s^(-1)` and no photoelectric effect is seen.

Step-by-step explanation:

To calculate the threshold frequency, we use the equation:

`E_k=h(\\u-\\u_o)`

where,

`E_k` = kinetic energy of the light =
`7.74* 10^(-20)J`

h = Planck's constant =
`6.626* 10^(-34)J.s`

`\\u` = frequency of the photon =
`6.66* 10^(14)s^(-1)`

`\\u_o` = threshold frequency of the sodium metal = ?

Putting values in above equation, we get:

`7.74* 10^(-20)=6.626* 10^(-34)(6.66* 10^(14)-\\u_o)\\\\\\u_o=5.49* 10^(14)s^(-1)`

Photoelectric effect is defined as the emission of electrons when light hits the surface of metal. This effect will be seen only when the incident light fallen on the metal is greater than the threshold frequency of the metal.

We know that:

Frequency of orange light =
`5* ^(14)s^(-1)`

It is visible, that frequency of incident light is less than the threshold frequency. So, the photoelectric effect will not be seen.

Hence, the threshold frequency of sodium metal is
`5.49* 10^(14)s^(-1)` and no photoelectric effect is seen.