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PhysicsModern PhysicsPhotoelectric effectHard2 minPYQ_2021

PhysicsHardstatement

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 a circular arc of radius $30 cm$ . The value of $B$ is ________ $\times 10^{- 7} T$ .
Given $h c = 20 \times 10^{- 26} J m$ , the mass of the electron $= 9 \times 10^{- 31} kg$ .

Answer:

125

Solution:

By photoelectric equation

$\frac{h c}{λ} - ϕ = k_{\max}$

$k_{\max} = \frac{1240}{500} - 1.25 \approx 1.25$

$r = \frac{\sqrt{2 m k}}{e B}$

$B = \frac{\sqrt{2 m k}}{e r}$

$= 125 \times 10^{- 7} T$

Stream:JEESubject:PhysicsTopic:Modern PhysicsSubtopic:Photoelectric effect

⏱ 2mℹ️ Source: PYQ_2021

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