Photons with energy of 2.95 eV illuminate a metal surface and it is found that voltage of 0.65 V is required to stop all the electrons that are ejected from the metal by this light.What is the metal?

Question

Quizplus · Accepted Answer

The work function (ϕ) of a metal is the minimum energy needed to eject an electron from the metal surface. The energy of the incoming photons is given as 2.95 eV. The stopping voltage (V_s) is the voltage needed to stop the ejected electrons, which is given as 0.65 V. The kinetic energy (KE) of the ejected electrons can be calculated using the equation KE = eV_s, where e is the charge of an electron (approximately 1.6 x 10^-19 C). Therefore, KE = 0.65 eV (since 1 eV = 1.6 x 10^-19 Joules, and here we are working directly in electron volts). The work function can be calculated using the photoelectric equation: ϕ = E_photon - KE, where E_photon is the energy of the incoming photons. So, ϕ = 2.95 eV - 0.65 eV = 2.3 eV. Potassium (K) has a work function close to this value, making it the correct choice.

Photons with Energy of 2