Question

The threshold wavelength of lithium is $8000\mathring{A}.$ When light of wavelength $9000\mathring{A}$ is made incident on it, then the photoelectrons

• A. Will not be emitted
• B. Will be emitted
• C. Will sometimes be emitted and sometimes not
• D. Nothing can be said

Answer 1

Answer: (A)

Will not be emitted

The wavelength of light is inversely proportional to its frequency, hence.
threshold frequency of lithium light is

${\nu }_0\propto \frac{1}{8000}$

and the frequency of incident light is
$\nu \propto 19000$
From above equations

$\frac{1}{8000}>\frac{1}{9000}$

$\Rightarrow {\nu }_0>\nu$
Since, threshold frequency is the minimum frequency due to which electron is able to knock out of the surface of metal. The incident frequency should be more than threshold frequency, therefore no photoelectrons will be emitted.

So, the answer is option (A)>