Question

The threshold wavelength for a surface having a threshold frequency of $0.6\times {10}^{15}$ Hz is :
given $c=3\times {10}^8$m/s

• A. 4000 $A^o$
• B. 6000 $A^o$
• C. 5000 $A^o$
• D. 3500 $A^o$

Answer 1

The correct option is C 5000 $A^o$

$\nu =\frac{C}{\lambda }$
So, ${\nu }_T=\frac{C}{{\lambda }_T}$

$\Rightarrow {\lambda }_T=\frac{C}{{\nu }_T}$

$=\frac{3\ast {10}^8}{0.6\ast {10}^{15}}$

$=5\ast {10}^{-7}m$
$=5000\ast {10}^{-10}m$
$=5000\mathring{A}$

So, the answer is option (C).