# I Photoelectric effect

1. Dec 9, 2016

### Leong

When the emitter is connected to the positive polarity of a battery, it is said that 'Some high speed electrons are still able to reach the collector and therefore there is flow of current.'

(1) What is the flow of electrons like in this case?

I thought electrons are supposed to flow from the negative polarity of the battery to the collector, to the emitter and finally to the positive polarity of the battery to produce a current.

(2) Why in this case, it is the other way round, yet it is said that there is a current?

2. Dec 9, 2016

### Hiranya Pasan

In this case kinetic energies of the electrons are concerned, If the falling photons have enough energies to give high kinetic energies to electrons, electrons can move to the collector, but the path may not be a linear path

3. Dec 9, 2016

### Leong

Would you mind explaining how the electrons flow in the circuit & how the current flows in the circuit?

4. Dec 9, 2016

### Hiranya Pasan

Im not sure about this answer but I think when polarity reversed there are some FREE electrons come back to the emitter due to the Coulomb potential, I think this the the reason to the flowing current in the circuit, because it is not possible to flowing current through the collector in this case.

5. Dec 9, 2016

### ZapperZ

Staff Emeritus
I'm trying to decipher what exactly is being asked here because some of the terms being used is a bit confusing.

Are you asking why, when you reverse-bias the cathode with respect to the anode, that there can still be a current flow in the "circuit"?

If this is the question, then this has more to do with the electronics. In a simple photoelectric experiment setup, one of the electrodes (either the cathode or the anode) has a "floating" potential. This allows for one to set a potential with respect to the other, but still allows for current to flow if charges either enter or leave it.

So for example, you may ground the cathode, and have the anode's potential to float. Then, you can reverse-bias the anode's potential, but any electrons that hits the anode are still flowing on that branch of the circuit, so current is registered. The built-in electronics allows that. The electrons that enter the anode do not make a closed loop back to the cathode. The circuit diagram that you see that often accompanies the photoelectric effect is highly simplified and often only a schematic representation of what is going on.

Zz.

6. Dec 13, 2016

### sophiecentaur

The elementary approach to the photoelectric effect only discusses the maximum energy of photo electrons. It's more complicated than that because of the range of actual energies of those electrons. The potential of the Anode will affect how many of the electrons make it to the anode and how many fall back to the emitter. The (reverse)":stopping potential" is the minimum that will stop the flow completely.