Question

The threshold wavelength for a surface having a threshold frequency of $0.6\times {10}^{15}$ Hz in ($\mathring{A}$) is

• A. $100$
• B. $2000$
• C. $5000$
• D. $400$

Answer 1

The correct option is C $5000$

$\begin{array}{c}given,\\ \text{threshold wavelength,}{\lambda }_0=\frac{c}{f}\\ c=\text{Speed of light}=3\times {10}^{8}ms\\ f=\text{frequency}=0.6\times {10}^{15}\\ =6\times {10}^{14}Hz\end{array}$

$\begin{array}{cc}\therefore {\lambda }_0& =\frac{3\times {10}^8}{6\times {10}^{14}}m\\ & =5\times {10}^{-7}m\\ & =5000\times {10}^{-10}m\\ & =5000\dot{A}\end{array}$