# What is the (a) momentum, (b) speed, and (c) de Broglie wavelength of an electron with kinetic energy of 120 eV.

Kinetic energy of the electron, Ek = 120 eV

Planck’s constant, h = 6.6 × 10−34 Js

Mass of an electron, m = 9.1 × 10−31 kg

Charge on an electron, e = 1.6 × 10−19 C

(a) For the electron, we can write the relation for kinetic energy as:

Where,

v = Speed of the electron

Momentum of the electron, p = mv

= 9.1 × 10−31 × 6.496 × 106

= 5.91 × 10−24 kg m s−1

Therefore, the momentum of the electron is 5.91 × 10−24 kg m s−1.

(b) Speed of the electron, v = 6.496 × 106 m/s

(c) De Broglie wavelength of an electron having a momentum p, is given as:

Therefore, the de Broglie wavelength of the electron is 0.112 nm.

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