Question

What is (a) the wavelength of a 4.90-eV photon and (b) the de Broglie wavelength of a 4.90-eV electron?

Answer 1

energy of a photon E = hc/L

h = planck's constant = 6.626*10^-34 Js

c = speed of light = 3*10^8 m/s

L = wavelength = ?

E = 4.9 eV = 4.9*1.6*10^-19 J

L = hc/E

L = (6.626*10^-34*3*10^8)/(4.9*1.6*10^-19)

wavelength = 253.55 nm <<<----------answer

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part(b)

kinetic energy K = P^2/(2m)

p = momentum = sqrt(2Km)

de Brogile wavelength = h/p

m = mass of electron = 9.11*10^-31

wavelength = h/sqrt(2Km)

given k = 4.9 eV = 4.9*1.6*10^-19 J

wavelength = 6.626*10^-34/sqrt(2*4.9*1.6*10^-19*9.11*10^-31)

wavelength = 55.44 nm <<<----answer