Question

The photo-electric threshold wavelength of tungsten is 2300 $A^o$. The energy of electrons ejected from the surface, if ultra-violet light of wavelength 1800 $A^o$ is incident on it, is

• A. 1.5 eV
• B. 2 eV
• C. 3.2 eV
• D. 6 eV

Answer 1

The correct option is A 1.5 eV

energy of ejected electrons $=$ incident energy - work function
$=\frac{hc}{{\lambda }_{uv}}-\frac{hc}{{\lambda }_T}$

$=\frac{1240}{180}-\frac{1240}{230}(hc=1240ev-nm)$

$=6.88-5.39$
$=1.49$
$\simeq 1.5ev$
So, the answer is option (A).