UV light of the wavelength 800 A and 700 A falls on the hydrogen atoms in their ground state and liberates electrons with KE 1.8 eV and 4 eV respectively. Calculate Planck's constant.

KE = hc/λ - W_f       where  W_f is work function

1.8 = hc / 8*10^-8  - W_f       .       ... (1)

4 = hc / 7*10^-8  - W_f                  ....(2)

2.2 = hc*10⁸ [1/7 - 1/8]

Plancks constat : h = 4.106 x 10^-15 eV-sec  or  6.578 x 10^-34 J-sec

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