Question

Surface #1 has work function j1, and when bombarded with photons of wavelength l1 emits photoelectrons with maximum energy KE1. Surface #2 has work function j2, and when bombarded by photons of wavelength l2 emits photoelectrons with maximum energy KE2.  If j1 >j2, then which of the following must be true?

1.KE1 >KE2

2.l1> l2

3.lC for surface #1 is greater than lC for surface #2.

4.lC for surface #2 is greater than lC for surface #1.

5.None of the above.

Answer 1

The equation of photoelectric effect is :

so,

  

and

if j1>j2, we cannot say anything about KE1 and KE2 unless we know the relation between l1 and l2.

So, first two options are out.

Now, if lC means cut-off wavelength (although it is not mentioned in the question), then we can find the relation between two cut-off wavelength from equation:

and

So, j1>j2, then clearly, lC2 > lC1.

Hence, option 4 is the correct answer.