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PhysicsModern PhysicsPhotoelectric effectEasy2 minPYQ_2020

PhysicsEasysingle choice

Lights of wavelengths $λ_{1} = 340 nm$ and $λ_{2} = 540 nm$ are incident on a metallic surface. If the ratio of the maximum speeds of the electrons ejected is $2$ , the work function of the metal is

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Solution:

$λ_{1} = 350 nm, λ_{2} = 540 nm, \frac{V_{1}}{V_{2}} = 2 \Rightarrow V_{1} = 2 V and V_{2} = V$

$\frac{hc}{λ_{1}} = ϕ + \frac{1}{2} m (2 V)^{2}$

$\frac{hc}{λ_{2}} = ϕ + \frac{1}{2} {mV}^{2}$

$\frac{hc}{λ_{1}} - \frac{hc}{λ_{2}} \times 4 = ϕ - 4 ϕ$

$hc (\frac{4}{540 nm} - \frac{1}{340 nm}) = 3 ϕ$

$ϕ = 1.8 eV$

Stream:NTA_ABHYAS_NEETSubject:PhysicsTopic:Modern PhysicsSubtopic:Photoelectric effect

⏱ 2mℹ️ Source: PYQ_2020

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