The surface of sodium metal is irradiated with radiation of wavelength x nm. The kinetic energy of ejected electrons is 2.8 10-20 J. The work function of sodium is 2.3 eV. The value of x is 102 nm. (Nearest integer) (Given : h = 6.6 10-34 J s; 1 eV = 1.6 10-19 J; c = 3.0 108 m s-1)
Answer
5
Solution
Energy of photon E = work function + KE
⇒ E = 2.3 1.6 10-19 + 2.8 10-20
= 3.68 10-19 + 0.28 10-19 = 3.96 10-19 J
= hcE = 6.6 10-34 3.0 1083.96 10-19
= 5.0 10-7 m = 500 nm = 5 102 nm
Answer: 5