Question 252: Dual Nature of Matter and Radiation

Question

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 ___________ $$	imes$$ 10$$-$$7 T. Given hc = 20 $$	imes$$ 10$$-$$26 J-m, mass of electron = 9 $$	imes$$ 10$$-$$31 kg

Accepted Answer

By photoelectric equation
$${{hc} \over \lambda } - \phi  = {k_{\max }}$$
$${k_{\max }} = {{1240} \over {500}} - 1.25 \approx 1.25$$
$$r = {{\sqrt {2mk} } \over {eB}}$$
$$B = {{\sqrt {2mk} } \over {er}}$$
$$ = 125 	imes {10^{ - 7}}T$$

Dual Nature of Matter and Radiation

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