### Video Transcript

A monochromatic light ray with
frequency π falls on a surface that has a critical frequency π sub c. If π is less than π sub c, which
of the following statements is true about the electrons on the surface? (A) By increasing the number of
photons, the number of the released electrons increases. (B) By increasing the number of
photons, the number of the released electrons decreases. (C) No electrons leave the
surface. (D) None of the answers are
correct.

We can answer this question by
recalling that the critical frequency, also known as the threshold or cut-off
frequency, is a property of a metal. It gives the minimum frequency of
an incident photon that can overcome that metalβs work function and induce the
photoelectric effect.

So, if incident photons have a
frequency that is greater than or equal to the threshold frequency, the
photoelectric effect will be induced and electrons will be emitted from the metal
surface. However, if incident photons have a
frequency thatβs less than the threshold frequency, the photoelectric effect will
not be induced and no electrons will leave the surface.

We are told in the question that
the frequency, π, of the monochromatic light ray is less than the critical
frequency of the surface, π sub c. So, it looks like the correct
answer is option (C): no electrons leave the surface. This means we can eliminate option
(D). But letβs quickly consider options
(A) and (B).

Since π is less than π sub c,
increasing the number of photons will have no effect on the number of electrons
released. Photons will still have the same
frequency π. And since this is still less than
the threshold frequency, π sub c, the photoelectric effect will not be induced and
no electrons will leave the surface. So, this means we can eliminate
options (A) and (B). Therefore, the correct answer must
be option (C). If photons with a frequency π that
is less than π sub c are incident on a metal surface, no electrons will leave the
surface.