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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 eVand 4.0 eV respectively. Find the value of Planck’s constant.

Radhika Batra , 10 Years ago
Grade 11
anser 1 Answers
Kevin Nash

Last Activity: 10 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 / λ1 λ2] =K.E.1 – K.E2
∴ h = (K.E. – K.E.­21 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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