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Question

A metal has a work function of 2.5×1019 J. What should be the threshold frequency beyond which if I shine light on the metal, photo electrons will come out?


A

3.8×1014Hz.

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B

2.3×1014Hz.

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C

3×1017Hz.

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D

none of these

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Solution

The correct option is A

3.8×1014Hz.


So, the work function of the metal is 2.5×1019J.

This means that we need to give an electron a minimum of 2.5×1019J of energy for it to come out of the metal. This energy needs to be supplied by light, in this case a photon.

So if the photon has a minimum energy of more than 2.5×1019J, then I am done.

Energy of a photon is hv

So hv2.5×1019J.

v2.5×1019h

v2.5×10196.626×1034

v3.8×1014Hz

So cut off frequency is 3.8×1014Hz.


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