Suppose there is a potential difference between the metal that ejects the electr

Question

Suppose there is a potential difference between the metal that ejects the electrons and the detection device, such that the detector is at a lower potential than the metal. The electrons slow down as they go from higher to lower electric potential; since they must overcome this potential difference to reach the detector, this potential is known as the stopping potential. To reach the detector, the initial kinetic energy of an ejected electron must be greater than or equal to the amount of energy it will lose by moving through the potential difference.

Suppose that two sets of values were recorded in this experiment:

Stopping potential V0 (V) Frequency f (Hz)

0.551 6×1014 0.965 7×1014

Using these data, extrapolate a numerical value for Planck's constant h.

Express your answer in Joule-seconds to 3 significant figures.

Explanation / Answer

the slope of the above data is,

m = dV/df = [0.965-0.551 / 7x1014 - 6x1014] = 4.14e-15 V/Hz

hence, the Planck's constant is,

h = me = 4.14e-15 * 1.602x10-19 = 6.63e-34 J.s

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