Question

calculate the kinetic energy of electronic when a light of wavelength 4 × 10*-7fall on the surface of a metal.Threshold wavelength of the metal is 8 ×10*-7
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Answer 1

Answer:

Explanation:

concept :

energy of photons E = hc/λ

where,

h is Plank's constant

c is the speed of light

λ is the wavelength of photons

(i) here, h = 6.626 × 10^-34 Js , c = 3 × 10^8 m/a

and λ = 4 × 10^-7 m .

Now,

E = 6.626 × 10^-34 × 3 × 10^8/4 × 10^-7 J

= 4.969 × 10^-19 J

we know,

1 ev = 1.602 × 10^-19 J

so, E = 4.969 × 10^-19 / 1.602 × 10^-19 ev

= 3.10 ev

(ii) according to Einstein photoelectric theory,

Kinetic energy = hv - hv₀

= 3.10 - 2.13 = 0.97 ev

(iii) Kinetic energy = 1/2mv² = 0.97 ev

1/2 × 9.11 × 10^-31 kg × v² = 0.97 × 1.602 × 10^-19J

v² = 0.97 × 1.602 × 10^-19 × 2 / 9.11 × 10^-31

= 0.341 × 10¹² m²/s²

v = 0.584 × 10^6 m/s