Question

The threshold frequency for photoelectric effect
on sodium corresponds to a wavelength of 5000
Å. Its work function is
(a) 4 × 10–⁻¹⁹ J (b) 1 J
(c) 2 × 10⁻¹⁹ J (d) 3 × 10⁻¹⁹ J

Answer 1

W=hc/lambda

h=6.6×10^-34J s

c=3×10^8m/s

lambda=5000Å=5×10^-7m

W=hc/lambda

={6.6×10^-34×3×10^8}/(5×10^-7)

=3.96×10^-19J