Question

The work function for a metal is $4eV$ to eject the photo electrons with zero velocity the wavelength of the incident light should be:

• A. $2700A^o$
• B. $1700A^o$
• C. $5900A^o$
• D. $3100A^o$

Answer 1

The correct option is D $3100A^o$

$E=h\nu =\frac{hc}{\lambda }$ work function W=4ev

Zero velocity $\Rightarrow E=W+K.E$

$E=W+O$

$E=W$

$\frac{hc}{\lambda }=W$

$\lambda =\frac{hc}{w}$

$\lambda =\frac{1240\frac{ev}{{nm}^{-1}}}{4ev}$ {hc is nearly to 1240$\frac{ev}{{nm}^{-1}}$}

$\lambda =310\left(nm\right)$

Wavelength of incident light is 310nm or $3100\stackrel{0}{A}$