Photoelectric effect

Question

Photoelectrons from a material with a binding energy of 2.71 eV are ejected by 420nm photons. Once ejected, how long does it take these electrons to travel 2.50 cm to a detection device?

Answer 1

Use 1/2 mv^2= hc/wavelength - binding energy to find the velocity of the  electrons.The time taken =d/v

Answer 2

Binding Energy is the work function .

K.E = Energy of Photon - Work Function

½mV² = hc/λ - Work Function

½(9.11x10^-31)V² = (6.63x10^-34)(3x10^8)/(420x10^-9) - 2.71(1.6x10^-19)

V = 296231.0953 m/s

Distance = Speed x Time

2.50x10^-2 = 296231.0953 x Time

Time = 8.439357108x10^-8 s ≈ 8.4x10^-8 s