Q. 275.0( 1 Vote )

A student performs an experiment on photoelectric effect, using two materials A and B. A plot of Vstop vs v is given in Fig. 11.2.



(i) Which material A or B has a higher work function?

(ii) Given the electric charge of an electron = 1.6 × 10–19 C, find the value of h obtained from the experiment for both A and B. Comment on whether it is consistent with Einstein’s theory :

Answer :

(i) Threshold frequency of material A (ν0A) = 5 x 1014 Hz

Threshold frequency of material B (ν0B) = 10 x 1014 Hz


Work function of any material is given by the product of Plank’s Constant and threshold frequency.



Since ‘h’ is constant, thus,



Thus, work function is directly proportional to the threshold frequency. Since, the threshold frequency of material B is greater than material A, thus material B has a higher work function.


(ii) The slope of the graph gives the value of h/e where ‘h’ is Plank’s Constant and ‘e’ is the charge on an electron.


For material A




For material B




Since, the value of h from experiment for metals A and B is different, thus, the experiment is not consistent with the theory.


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