A light beam of wavelength 500 nm is incident on a metal having work function of 1.25 eV, placed in a magnetic field of intensity B. The electrons emitted perpendicular to the magnetic field B, with maximum kinetic energy are bent into circular are of radius 30 cm. The value of B is ___________ $\times$ 10$-$7 T.
Given hc = 20 $\times$ 10$-$26 J-m, mass of electron = 9 $\times$ 10$-$31 kg
Answer (integer)
125
Solution
By photoelectric equation<br><br>${{hc} \over \lambda } - \phi = {k_{\max }}$<br><br>${k_{\max }} = {{1240} \over {500}} - 1.25 \approx 1.25$<br><br>$r = {{\sqrt {2mk} } \over {eB}}$<br><br>$B = {{\sqrt {2mk} } \over {er}}$<br><br>$= 125 \times {10^{ - 7}}T$
About this question
Subject: Physics · Chapter: Dual Nature of Matter and Radiation · Topic: Photoelectric Effect
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