Question

Photons of wavelength 199 nm are incident on a metal plate in a photocell, and electrons are ejected. A stopping potential of 1.10 V is able to just prevent any of the ejected electrons from reaching the opposite electrode. What is the maximum wavelength of photons that will eject electrons from this metal

Answer 1

Answer:

λ = 11.29 x 10⁻⁷ m = 1129 nm

Explanation:

According to the law of conservation of energy:

$Photon\ Energy = Energy\ Applied\ by\ Stopping\ Potential\\\\\frac{hc}{\lambda} = eV\\\\\lambda = \frac{hc}{eV}$

where,

λ = maximum wavelength = ?

h = Plank's Constant = 6.625 x 10⁻³⁴ J.s

c = speed of light = 3 x 10⁸ m/s

e = charge on electron = 1.6 x 10⁻¹⁹ C

V = stopping poteential = 1.1 V

Therefore,

$\lambda = \frac{(6.625\ x\ 10^{-34}\ J.s)(3\ x\ 10^8\ m/s)}{(1.6\ x\ 10^{-19}\ C)(1.1\ V)}$

λ = 11.29 x 10⁻⁷ m = 1129 nm