# Homework Help: Photoelectric effect and photocurrent drop

1. Nov 23, 2008

### hayyan1

1. The problem statement, all variables and given/known data

Does the photocurrent drop to zero when a potential across it is equal to the kinetic energy of electrons?, because i found this not to be the case, the photocurrent reached a steady value that didnt decrease further, as i increased the potential across the anode and cathode. I dont understand why this happend?

2. Nov 24, 2008

### Redbelly98

Staff Emeritus
Was the anode at + or - relative to the cathode?

3. Nov 24, 2008

### hayyan1

anode voltage was increased negatively so electron should be repelled from anode in theory, but for some reason i still was obtaining postive photocurrent, maybe i should have taken much larger negative values for potential, so current would eventually become zero?, however do you think i can extrapolate (with a curve of best fit) to zero current, because my graphs are curving towards zero photocurrent.

4. Nov 24, 2008

### Redbelly98

Staff Emeritus
It depends. What wavelength(s) was/were used to generate the photocurrent? How high a voltage did you get to?

Extrapolating reasonably depends on whether graphing the data generates a straight line. Does it?

5. Nov 24, 2008

### hayyan1

I used yellow, turquoise, green, blue, violet. it isnt ment to generate a straight line, for each frequency, the photocurrent (yaxis) is kind of meant to drop like a 1/x graph when plotted against the potential across the xaxis

6. Nov 24, 2008

### Redbelly98

Staff Emeritus
That's weird. I would expect current to be zero if you go high enough in voltage, but I haven't done the experiment.

Not sure what's going on.