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Grade 11Modern Physics

Ultraviolet light of wavelengths 800 Å when allowed to fall on hydrogen atoms in their ground state is found to liberate electrons with kinetic energy 1.8 eV and 4.0 eV respectively. Find the value of Planck’s constant.

Radhika Batra

12 Years agoGrade 11

1 Answer

Kevin Nash

12 Years ago

hc / λ₁ – hc / λ₀ = K.E. ₁ ….(i)

And hc / λ₂ – hc / λ₀ = K.E.₂ ….(ii)

⇒ hc / λ₁- hc / λ₂ = K.E.₁ – K.E₂

⇒ hc [λ₂ - λ₁/ λ₁λ₂] =K.E.₁ – K.E₂

∴ h = (K.E.₁ – K.E.₂)λ₁ λ₂ / c (λ₂ – λ₁)

= (1.8 – 4) x 1. 6 x 10^-19 x 800 x 10^-10 x 700 x 10^-10 / 3 x 10⁸ x (700 - 800) x 10^-10

= 6.6 x 10³⁴ J.s.

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