In a photocell bichromatic light of wavelengths 2475 A and 6000 A are incident on cathode whose work function is 4-8 e V- If a uniform magnetic field of 3 - 10 - 5 Tesla exists parallel to the plate- the radius of the path describe by the photoelectron will be mass of electron -9- 10 -31 kg

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Analysis of Force Equation

In a photocel...

Question

In a photocell bichromatic light of wavelengths $2475 ˚ A$ and $6000 ˚ A$ are incident on cathode whose work function is $4.8 e V .$ If a uniform magnetic field of $3 \times 10^{- 5}$ Tesla exists parallel to the plate, the radius of the path describe by the photoelectron will be (mass of electron $= 9 \times 10^{- 31} k g$ )

1 c m

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5 c m

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10 c m

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25 c m

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Solution

The correct option is B $5 c m$
Energy of photons corresponding to light of wave length $λ_{1} = 2475 A^{o}$ is $E_{1} = \frac{12375}{2475} = 5 e V$ .
and that corresponding to $λ_{2} = 6000 A^{o}$ is
$E_{2} = \frac{12375}{6000} = 2.06 e V$
As $E_{2} < W_{0}$ and $E_{1} > W_{0}$
Photoelectric emission is possible with $λ_{1}$ only. Maximum kinetic energy of emitted photoelectrons $K = E - W_{0} = 5 - 4.8 = 0.2 e V$
Photo electrons experiences magnetic force and move along a circular path of radius
$r = \frac{\sqrt{2 m k}}{Q B} = \frac{\sqrt{2 \times 9 \times 10^{- 31} \times 0.2 \times 1.6 \times 10^{- 19}}}{1.6 \times 10^{- 19} \times 3 \times 10^{- 5}}$
$= 0.05 m = 5 c m$ .

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In a photocell bichromatic light of wavelengths 2475˚A and 6000˚A are incident on cathode whose work function is 4.8eV. If a uniform magnetic field of 3×10−5 Tesla exists parallel to the plate, the radius of the path describe by the photoelectron will be (mass of electron =9×10−31kg )