Addressing a common misconception about the photoelectric effect

[@waynewong7607]

Hi Paul - really glad you've made an articulate video to deal with this issue, as I know it's a point of debate amongst many Physics teachers. Your interpretation certainly makes the most sense in terms of energy. I've tried to test this using the popular PHET photoelectric simulator. This interpretation would predict that as the frequency of light is increased, while intensity is kept constant, the photocurrent should decrease. However, the simulator shows the opposite to occur. This could potentially just be an artifact of the simulator, but I have tried and failed to find real world experimental data to help validate this. Would love to hear your thoughts on this.

[@leonhardtkristensen4093]

I would really have liked him to answer your question too. If you still have access to the equipment (I have no equipment so must relay on others) could you try to test it a bit more. I believe that red light (low frequency light) can't release any electrons. I really thought that that was part of Albert Einstein's postulation - and that was at any intensity. It is only blue light and higher frequencies photon's that can release electrons I believe. What I would believe is happening for you is that your light frequency may not be pure meaning that only some of your light photons have high enough energy to release electrons and when you increase your frequency more photons get above the threshold. Are you sure that your power input is kept constant? Constant power input but higher light frequency must give less photons. That would look like lower light intensity too I believe. Our eye's are not linear at different frequencies so a light meter should be used I believe. What I would like you to do if you can retest is to make sure that your frequency is high enough before you start to increase the frequency and also keep your energy input constant not your light intensity constant. Then I believe you should get the correct decreasing of the current I believe. If any body else can answer these questions feel free to reply.

[@HackErDUO]

follow

[@youtubethunder6116]

You explained Better than my physics teacher

[@marcrindermann9482]

I wouldn't necessarily say it's a misconception if the model taught is limited on changing the number of photons only and not the frequency. What you did here is expanding the view that many students may have had by changing the parameters.

[@VanshPBedi]

Thanks physics high

[@simonmoore992]

Looks like I need to update my 7.3 Topic Book. Actually, I do have a question. When intensity is kept constant, if the kinetic E of the photoelectrons increases with an increase in photon frequency doesn't that offset the current drop caused by the reduced number of photons incident upon the metal?

[@MillzOT.]

Thanks papa physics great vid dad❤️🧛🏿‍♂️

[@Vineger23]

So if you want intensity to remain the same then increasing frequency, current decreases. But if you do no care about intensity then by increasing frequency, intensity increases as well.

[@AraDeanMaffy]

EM-waves with frequency f and amplitude A hit the cathode. I always thought increasing the amplitude of an EM-wave increases the Intensity but doesnt free more electrones - since the frequency doesnt change. How does this match with your explanation of in/decreasing numbers of photons? Where is my misconception/mistake?

[@davehughes7332]

I think the misconception is in treating light as a continuous wave rather than as discrete photons. That was Einstein's insight which allowed him to explain the photoelectric effect. You do get more photoelectrons with an increase in intensity, but the maximum kinetic energy doesn't change unless the frequency does.

[@NoNameAtAll2]

amplitude is energy energy is energy of single particle times number of particles energy of single photon is frequency so if you increase aplitude, but don't change frequency, you get more particles

[@leonhardtkristensen4093]

I think you are thinking about when you look at it on an oscilloscope. The ac wave you see does increase in amplitude but there it is the voltage you increase = number of electrons at that point compared to another point. As other have said what increases with power RADIATED (what light or radio signals are) is the number of photons. EM waves when radiated are photons. Amplitude doesn't really mean any thing in a light beam. Intensity does and that is the number of photons coming. If you measure the intensity of a light beam it is voltage you are measuring again.

[@physics_pratibha]

Sir then why we say current don't change if intensity does not change? please help me out.

[@PhysicsHigh]

Because usually the precondition is that we have the same frequency.

[@physics_pratibha]

Sir I am convinced with the logic you explained and that is why I feel when frequency increases but intensity remains constant,there should be some decrease of current as number of photons incident ing reduce .But that is not mentioned by the scholars who worked on this experiment.I am in little confusion sir.

[@h7opolo]

0:59 australian accents are not conducive to explaining electricity since they omit the pronunciation of "r"s resulting in the word "current" sounding like a dirty word.

[@monsieurmitosis]

That was some type of editing glitch. I really don't think Australians are guilty of what you are saying, in general. I notice a lot of British people soften their Rs, or replace their double Ls with more of a W sound...even if it's not the result of an actual speech impediment.

[@h7opolo]

4:26 "fewer PE emitted," not "less..."

[@AhmedMohammed-ik8ew]

first view

[@Pierluigi_Di_Lorenzo]

It's resonance, not quanta.