Physics Question about photodiodes

chris241111

Draw a diagram of a circuit that could be used to show the operation of a photodiode? came up in a mock paper, just wondering how to do this and which componant I should put in, resistors etc, thanks

thetalker

Do you mean a photocell? because if so its in doodle-physics, assuming you have that.
Unless its in the optional chapters, then I wouldn't know.

A97

Is that the Applied Electricity section? I didn't do that for Leaving Cert but I'm currently doing engineering in college so I do know a little bit about photodiodes.

I would draw a circuit with a voltage source with a photodiode in reverse bias so that current doesn't flow. Add in a galvanometer too.

Then draw the same circuit with an external light source. Show that the galvanometer has moved, meaning current is flowing. I don't think a resistor would be required since the currents generated by photodiodes aren't too high.

If you wanted to get specific, you could maybe replace the galvanometer with a bell, and call it a burglar alarm.

chris241111

Thanks for the clear explanation, yes I think its in the applied electricity section and probably a mistake on the mock paper to include it in Q12.

Would you happen to know the answer to the question that follows this one,

An alternating current of very low frequency(e.g. 1hz) is supplied to a light emitting diode, what is observed when the current is switched on? explain your answer.

Do led's prefer low or high frequency I can't find anything in the book on this.

A97

chris241111 wrote: »

Thanks for the clear explanation, yes I think its in the applied electricity section and probably a mistake on the mock paper to include it in Q12.

Would you happen to know the answer to the question that follows this one,

An alternating current of very low frequency(e.g. 1hz) is supplied to a light emitting diode, what is observed when the current is switched on? explain your answer.

Do led's prefer low or high frequency I can't find anything in the book on this.

There could be some principle that I'm forgetting here, but what I would assume is that if the frequency is 1 Hz, the current would be forward biased for one second, then reversed the next. So the LED would flicker on and off each second. If the frequency is sufficiently high, the human eye would not be able to detect the flickering as it is so fast, giving the impression that the LED is always on.

chris241111

A97 wrote: »

There could be some principle that I'm forgetting here, but what I would assume is that if the frequency is 1 Hz, the current would be forward biased for one second, then reversed the next. So the LED would flicker on and off each second. If the frequency is sufficiently high, the human eye would not be able to detect the flickering as it is so fast, giving the impression that the LED is always on.

thanks yes that makes so much sense, have you considered a career in teaching:D

A97

chris241111 wrote: »

thanks yes that makes so much sense, have you considered a career in teaching:D

I do like helping people with these kinds of things, especially coming up to exam time since at the moment, you guys need to bring as much information to the forefront of your brain as possible. I'm happy to facilitate that. I know what it's like not to understand very much, and I don't want others to get that feeling if I can.

I could potentially go into teaching, but I'm not sure how good I'd be getting the point across to students who don't want to be there, which is a pity since they are the ones who could do with the most help.