KVPY Sample Paper KVPY Stream-SX Model Paper-30

All electrons ejected from a surface by incident light of wavelength 200 nm can be stopped before travelling 1 \[m\] in the direction of uniform electric field of 4 N/C. The work function of the surface is:

A) 4 eV

B) 6.2 eV

C) 2 eV

D) 2.2 eV

Correct Answer: D

Solution :

The electron ejected with maximum speed \[{{V}_{\max }}\] are stopped by electric field E=4N/C after traveling a distance d = 1m

\[\therefore \,\,\,\frac{1}{2}mV_{\max }^{2}=eEd=4\,eV\]

The energy of incident photon \[=\frac{1240}{200}\]\[=6.2\,\,eV\]

From equation of photo electric effect

\[\frac{1}{2}mv_{\max }^{2}=hv-{{\phi }_{0}}\]

\[\therefore \,\,\,{{\phi }_{0}}=6.2-4=2.2\,\,eV\]