Question

A beam of electromagnetic radiation of intensity 6.4 × 10^–5 W/cm² is comprised of wavelength, λ = 310 nm. It falls normally on a metal (work function φ = 2eV) of surface area of 1 cm². If one in 10³ photons ejects an electron, total number of electrons ejected in 1 s is 10^x. (hc=1240 eVnm, 1eV=1.6×10^–19 J), then x is ___.

Answer 1

Energy of proton E = 1240/310 = 4eV > 2eV (so photoelectric effect will take place)

= 4 × 1.6 × 10^–19 = 6.4 × 10^–19 Joule

No of photoelectron emitted per second

= 10¹⁴/10³ = 10¹¹

Answer 2

Power incident P = I x A

n = no. of photons incident /second

nE_ph = IA

n = 10⁺¹⁴ per second

Since efficiency = 10^–3

no. of electrons emitted = 10⁺¹¹ per second.

x = 11.