A monochromatic light is incident on a metallic plate having work function ϕ . An electron, emitted normally to the plate from a point A with maximum kinetic energy, enters a constant magnetic field,

Question

A monochromatic light is incident on a metallic plate having work function $ϕ$ . An electron, emitted normally to the plate from a point $A$ with maximum kinetic energy, enters a constant magnetic field, perpendicular to the initial velocity of electron. The electron passes through a curve and hits back the plate at a point $B$ . The distance between A and B is :
(Given : The magnitude of charge of an electron is e and mass is $m, h$ is Planck's constant and c is velocity of light. Take the magnetic field exists throughout the path of electron)

Options:

Answer:

C

Solution:

$KE_{m a x} = \frac{hc}{λ} - ϕ p = 2 mK_{m a x} p = 2 m (\frac{hc}{λ} - ϕ) d_{A - B} = 2 R = 2 [\frac{p}{qB}]$
$d_{AB} = \frac{2 2 m ( \frac{hc}{λ} - ϕ )}{eB} = \frac{8 m ( \frac{hc}{λ} - ϕ )}{eB}$

TestHub · Accepted Answer

​ KE m a x ​ = λ hc ​ − ϕ p = 2 mK m a x ​ ​ p = 2 m ( λ hc ​ − ϕ ) ​ d A − B ​ = 2 R = 2 [ qB p ​ ] ​ d AB ​ = eB 2 2 m ( λ hc ​ − ϕ ) ​ ​ = eB 8 m ( λ hc ​ − ϕ ) ​ ​

Physics - Modern Physics Question with Solution | TestHub

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