Question

Blue light is falling on metal surface causing ejection of electrons with stopping potential $1\text{eV}$. If yellow light falls on metal instead of blue, the maximum kinetic energy (approximately) equal to,

• A. $1\text{eV}$
• B. $4\text{eV}$
• C. $1.2\text{eV}$
• D. zero; i.e. no emission

Answer 1

The correct option is D zero; i.e. no emission

$(K.E{)}_{max}=\frac{hc}{\lambda }={\varphi }_0$
If $(K.E{)}_{max}=V_s=1\text{eV}$, that's very small and also ${\lambda }_{yellow}>{\lambda }_{blue}$
$\therefore$ No emission will take place
$\therefore$ Option $\left(D\right)$ is the correct answer.

$\begin{array}{c}\text{Why this question?}\\ \text{This is an example of, "there is no emission above threshold wavelength."}\end{array}$