Question

The work function of substance is $4eV$, then which of the following cannot cause photoelectric emission from the substance ? $(hc=1242eV-nm)$

• A. $\lambda =200nm$
• B. $\lambda =300nm$
• C. $\lambda =400nm$
• D. $\lambda =250nm$

Answer 1

The correct option is C $\lambda =400nm$

For emission, $\frac{hc}{\lambda }>\Phi \frac{1242}{\lambda }>4\frac{1242}{4}>\lambda \lambda <310nm$

So if $\lambda$ is less than $310nm$, we will see photoelectric emission.