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  • Following results are observed when sodium metal is irradiated with different wavelengths. Calculate (b) Planck’s constant.

2.52    Following results are observed when sodium metal is irradiated with different wavelengths. Calculate (b) Planck’s constant.

\\\lambda\ (\textup{nm})\qquad \qquad \qquad 500\quad 450\quad 400\\ \textup{v}\times 10^{-5} \ (\textup{cm s}^{-1})\quad \; 2.55\ \ 4.35\ \ 5.35

Answers (1)

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We have the threshold wavelength.\lambda_{o} = 540\ nm

Then substituting this value in any of the equation ( look in the previous part), we get

\left ( \frac{hc}{10^{-9}} \right )\left ( \frac{1}{400}-\frac{1}{\lambda} \right )= \frac{1}{2}m(5.35\times10^3)^2

\left ( \frac{hc}{10^{-9}} \right )\left ( \frac{1}{400}-\frac{1}{540} \right )= \frac{1}{2}m(5.35\times10^3)^2

Taking the mass of an electron to be 9.11\times10^{-31}kg.

h= \frac{(9.11\times10^{-31})(5.35\times10^3)^2\times10^{-9}\times(400\times540)}{2\times(3.0\times10^8)(140)}

= 6.705\times10^{-34} Js  approximately.

Posted by

Divya Prakash Singh

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