In a photoelectric experiment it is found that a stopping potential of 1.00 v is needed to stop all the electrons when incident light of wavelength 278 nm is used and 2.6 v is needed for light of wavelength 207 nm. from these data determine planck's constant and the work function of the metal.

Planck’s constant is

work function of metal is

Explanation:

The maximum kinetic energy from electron from photoelectric effect is given by

where  is applied voltage and e is charge on electron and substituting charge on electron by  and 1.00 V for  

Considering that the wavelength, \lambda of light used is given as

Energy of light is given by

  where  is the wavelength, h is Planck’s constant and c is speed of light. Taking c for  

Substituting values of wavelength and speed of light we obtain

If work function is  then

 hence

------- Equation 1

Energy corresponding to wavelength of 207 nm is

Maximum kinetic energy of electrons when  is 2.6 V becomes

From  and substituting  for E and  for  we have

------ Equation 2

Equation 2 minus equation 1 gives

Therefore, Planck’s constant is

Recalling equation 1 and substituting back the value of h as obtained

Therefore, work function of metal is

- measure reactants precisely. ( first choice)

- stir to the reaction take place. ( second choice)

- wait patiently until the reaction completes. ( fourth choice)

- make sure to recover as much copper as possible. ( last choice)

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