# Is photocell current equal zero at threshold frequency?

In photocell is there currant at threshold frequency $$f=f_o$$? I mean $$I=0$$ at $$f=f_o$$? • It mack difference if i use a voltage between cathode and anode in this case f=fo Threshold frequency Is currant = zero also or what? – Mohammed A. Shabak Jun 15 at 21:08
• I'm sorry i want more explanation if the f= fo "threshold frequency" and voltage>0 is current =zero? – Mohammed A. Shabak Jun 16 at 10:33
• Thank you i got it. 1- Then if i apply Threshold frequency and positive voltage the current > zero. 2- f0 threshold fthr?? – Mohammed A. Shabak Jun 16 at 15:08

The incident photons can excite electrons from the valence zone into the conducting zone. All electrons that are at most $$|f_{inc} - f_0|$$ below the edge of the valence zone are eligible. But, if these two exactly coincide, then the thickness of that layer of the zone is zero, and there are no electrons that can jump, so yes, exactly at the threshold, the current is zero. However, since no source of light can give single perfect frequency, in practice this threshold will look smoother if you use, say, a laser with tunable frequency.
EDIT 2: Oh, now I get the question, I misunderstood it at first, sorry. From what I get, you apply photons and also electric current. Both try to excite the electron from one zone to another. Together, they must supply energy equal to $$h f_{0}$$ Then, the photocurrent appears iff $$h f_{inc} + |e|V > h f_{0}$$.
Changed the notation to fit the question, $$f_0$$ is threshold frequency, $$f_{inc}$$ is the incident frequency.