Department of Pre-University Education, KarnatakaPUC Karnataka Science Class 12

# Find the Maximum Magnitude of the Linear Momentum of a Photoelectron Emitted When a Wavelength of 400 Nm Falls on a Metal with Work Function 2.5 Ev. - Physics

Sum

Find the maximum magnitude of the linear momentum of a photoelectron emitted when a wavelength of 400 nm falls on a metal with work function 2.5 eV.

(Use h = 6.63 × 10-34J-s = 4.14 × 10-15 eV-s, c = 3 × 108 m/s and me = 9.1 × 10-31kg)

#### Solution

Given :-

wavelength of light , λ = 400  "nm" = 400 xx 10^-9  "m"

Work function of metal, phi = 2.5  "eV"

From Einstein's photoelectric equation,

Kinetic energy = (hc)/λ - phi

Here, c = speed of light

h = Planck's constant

therefore K.E. = (6.63 xx 10^-34 xx 3 xx 10^8)/(4 xx 10^-7 xx 1.6 xx 10^-19) - 2.5  "eV"

= 0.605   "eV"

Also , K.E. = p^2/(2m)

where p is momentum and m is the mass of an electron.

therefore p^2 = 2"m" xx K.E.

⇒ p^2 = 2 xx 9.1 xx 10^-31 xx 0.605 xx 1.6 xx 10^-19

⇒ p = 4.197 xx 10^-25  "kg - m/s"

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#### APPEARS IN

HC Verma Class 11, Class 12 Concepts of Physics Vol. 2
Chapter 20 Photoelectric Effect and Wave-Particle Duality
Q 17 | Page 365