Photons of frequencies 2.2 × 10^15 Hz and 4.6 × 10^15 Hz are incident on a metal surface. The corresponding stopping potentials….

Q. Photons of frequencies 2.2 × 10¹⁵ Hz and 4.6 × 10¹⁵ Hz are incident on a metal surface. The corresponding stopping potentials were found to be 6.6V and 16.5V respectively. Given e = 1.6 × 10^-19 c, the value of universal Planck’s constant is

(a) 6.6 × 10^-34 Js

(b) 6.7 × 10^-34 Js

(c) 6.5 × 10^-34 Js

(d) 6.8 × 10^-34 Js

Ans: a

Sol: hν = φ + eV₀
h × 2.2×10¹⁵ = φ + e × 6.6   …..(i)

h × 4.6×10¹⁵ = φ + e × 16.5   …..(ii)

Subtracting (i) from (ii)

h(4.6 −2.2)× 10¹⁵ = e(16.5 −6.6)

h = e ×9.9/(2.4×10¹⁵) = 1.6×10^-19 ×9.9/(2.4×10¹⁵)

h = 6.6 × 10^-34 Js