If light of wavelength 412.5 nm is incident on each of the metals given below, which ones will show photoelectric emission?
|
Metal |
Work Function (eV) |
|
Na |
1.92 |
|
K |
2.15 |
|
Ca |
3.20 |
|
Mo |
4.17 |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Na and K only
Energy of incident photon:
$ E = \frac{hc}{\lambda} = \frac{1240 \ \text{eV·nm}}{412.5 \ \text{nm}} $
$ E = 3.01 \ \text{eV} $
Compare with work functions:
Na : $1.92 \ \text{eV} \lt 3.01 \ \text{eV} $ → emission occurs.
K : $2.15 \ \text{eV} \lt 3.01 \ \text{eV} $ → emission occurs.
Ca : $3.20 \ \text{eV} \gt 3.01 \ \text{eV} $ → no emission.
Mo : $4.17 \ \text{eV} \gt 3.01 \ \text{eV} $ → no emission.
Metals showing photoelectric emission: Na and K.