Question

16) An ultraviolet light of wavelength 2000 A irradiates a photocell made of molybdenum metal. If the
stopping potential is - 1.5 V. what is the work function of the metal?
(Planck's constant = 6.6 X 10-34 / s)
a) 2.5 x 10-19 11) 5.0 x 10 11 c) 7.5x 10-191 d) 1 x 10-181
​

Answer 1

Given :

Wavelength of UV light, w = 2000 Å

Stopping potential, V = -1.5 V

Planck's constant, h = 6.6 X 10-34 / s

To find :

The work function of the metal, W

Solution :

• We know that,

eV = hc/w - W

• Substituting all values in above formula

W = hc/w - eV

= (6.6×10^-34×3×10^8/2000×10^-10) - 1.6×10^-19×(-1.5)

= ( 19.8×10^-26 / 2×10^-7 ) + 1.6×1.5×10^-19

= 9.9×10^-19 + 2.4×10^-19

= ( 9.9 + 2.4 ) × 10^-19

W = 12.3×10^-19