How Does Distance Affect Photocell Output?

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The discussion focuses on how to measure the output of a photocell in relation to the distance from a light source. Participants suggest connecting the photocell to an ammeter to measure current, emphasizing the importance of conducting the experiment in a dark room with a single light source. The inverse square law is highlighted as a key concept, explaining how light intensity decreases with distance. Suggestions for improving the experiment include plotting current against distance and considering safety precautions, although the voltages involved are low. Overall, the conversation provides practical advice for conducting the experiment and understanding the underlying physics.
  • #51
hiya, i have to do the same piece of work but I want to write a bit about infrared radiation in atmosphere and how that can affect my results. I'm also a bit confused on why i should have a voltmeter in the circuit and not just an ammeter. could anyone help!

thanx
 
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  • #52
i also would like to know whether the experiment has anything to do with the photoelectric effect.
 
  • #53
ii would like to share my thoughts.Iam in eistein's situation atm. My assignment made me waste a lot alot of hours researching and outcome I am confusing so bad at the same time clear up something and headaches. Sometime u just have to take the short cut way by asking directly:p. Any help would b kindly though. BTW i just went on dis forums few days ago. I wonder where r u people from(the majority). Like i been searching though forums i find things i neva heard b4 or maybe it advance coarse?. I live in Australia>.>
 
  • #54
so do you now anything about the work.

england
 
  • #55
hiya ekinnike, do you know what you call a point source of radiation- i mean apparatus you'd use for infrared radation source
 
  • #56
anapatel said:
hiya ekinnike, do you know what you call a point source of radiation- i mean apparatus you'd use for infrared radation source
hello, sadly i kno hardly any solid physics. Sorry can't help u.
 
  • #57
I think the photocell gives an output due to the photoelectric effect
Anyways...
OI mate (einstein) its exactly what bytefire said right? I found this the same way as bytefire did and this is the planning exercise I've got to hand in on the 17th, u're grateful in a way that u acknowledge the help u're given but at least put it together yourself, u lazy bum.

U are "Lei sai po"

Btw, thanks for the help here, I've gained more than enough background info. Cheers!
 
  • #58
im doing the same experiment, should i explain anything about the photoelectric effect or just mention?
 
  • #59
:rolleyes: My teacher said we only need to know the background, so I think I might mention it ie how photocell works..
 
  • #60
anapatel said:
hiya ekinnike, do you know what you call a point source of radiation- i mean apparatus you'd use for infrared radation source
How about a flame? Like from a Bunsen burner. Or a small light bulb.
 
  • #61
Voltmeter?

Hi, I am doing the planning exercise aswell.

Would a voltmeter be ok to measure the output of the photocell because voltage is proportional to resistance ( which varies with amount of infrared radiation shone on it)?
Thanks, Lewis
 
  • #62
lewmang said:
Hi, I am doing the planning exercise aswell.

Would a voltmeter be ok to measure the output of the photocell because voltage is proportional to resistance ( which varies with amount of infrared radiation shone on it)?
Thanks, Lewis
No, you can't use a voltmeter directly. You can put an explicit resistor in series with the photodiode, and measure the voltage drop across the resistor from the photocurrent.

Check the accuracy and sensitivity specs for your DVM, and check the specs for the output photocurrent that you expect from your photodiode/photocell. Then figure out which method will give you the best data...
 
  • #63
thanks for the quick reply.
Ok, so ill use a fixed resistor in series with the LDR, would an LDR pick up infrared radiation?
And what kind of voltage would be needed to put through the currents.
By the way i don't hav to actually do the experiment i have to design it with some theory as evidence for my actions.
 
  • #64
*wht kind of voltage would be needed to send through the circuits
 
  • #65
I didn't say use a resistor in series with a Light Dependent Resistor. As for the IR sensitivity of LDRs, I have no idea. As part of your project, you need to find and read the datasheets for the various light sensing component technologies, and list the advantages and disadvantages of each. That will guide your choice as to which one to use for the IR sensor experiment.
 
  • #66
what do you mean by datasheets? We havn't been given any data to use it is basically start from scratch
 
  • #67
lewmang said:
what do you mean by datasheets? We havn't been given any data to use it is basically start from scratch
Use the Internet. Use google some, look for companies that manufacture the components that you are considering, download the PDF datasheets for the components, and start reading the specifications. That's how it works in the real world after school...

Like, I just googled +photodiode +IR and got lots of hits. Here's the first one:

http://photodiode.globalspec.com/Industrial-Directory/photodiode_ir
 
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  • #68
I read earlier on in the thread that you said maybe use a small balb, would this be sufficient too?
 
  • #69
what kind of photocell would be needed to measure infrared radiation that would be available in schools?
 
  • #70
What do you mean by "available"? You mean like what can you take apart to pull out a photocell for experiments (like an elevator door sensor, or somebody's camera light sensor)? Won't you get in trouble if you start taking things apart at school? Or do you mean some part that is easy to order from a place like Digikey.com?
 
  • #71
lewmang, u'll have to ask your physics teacher about that...
 
  • #72
ok, also what kind scale of voltmeter would be needed and how would i know what scale to use? I will set the powerpack to let's say 6V on each circuit.
 
  • #73
would a voltmeter that reads to 5V be ok?
 
  • #74
please answer it has to be in for tomorrow
 
  • #75
So what photodiode/photocell/LDR did you pick for your project? What does the datasheet say about the output characteristics of the device? That will guide what instrument you use for the experiment, and what kind of accuracy you can expect, and what distance ranges you can expect to cover. Do the work.
 
  • #76
there is no datasheet, the physics teacher just said we can use an ordinary photocell, maybe i should just say i will choose an according voltmeter after tryin the experiment with a 0-20V voltmeter
 
  • #77
Well, you need to do this. Go to www.Digikey.com and type photocell into the search box. You will get 32 hits, sorted by output type. You can apply some filters to the results if you like, and in the end, download and *read* a couple of their datasheets. You might even do something radical and note the vendor name, and go to their website and look for Application Notes or other information that will help you write up a cohesive and knowledgeable report. That's how we do it in the world after school, so it's good for you to start getting some practice on it. Good luck.
 
  • #78
i don't understand what a 20K Ohm at 10 lux photocell, all i know is i think it creates a voltage when light is shone on it
 
  • #79
does the circuit with the photocell need a power supply or does the photocell produce a flow of electricity?
 
  • #80
lewmang said:
i don't understand what a 20K Ohm at 10 lux photocell

This means that when the photodiode is exposed to light of intensity 10 lux it has a resitance of 20K ohms. This is alos its maximum resistance.

lewmang said:
does the circuit with the photocell need a power supply or does the photocell produce a flow of electricity?

Depends what circuit you are using, if you are connecting your photodiode directly to an ammeter, then no power supply is required, however, if you are using a current to voltage converted (Op amp), then you will need a supply.

~H
 
  • #81
can i connect a voltmeter directly to the photocell?
 
  • #82
im using a photovoltaic cell, would it be ok to measure the voltage with this with a circuit with just the cell and a voltmeter?
 
  • #83
bigbadcityboy said:
im using a photovoltaic cell, would it be ok to measure the voltage with this with a circuit with just the cell and a voltmeter?
No. You need to measure the photocurrent.
 
  • #84
but a solar cells voltage output stays the same but it outputs a curent?
 
  • #85
surely the 'voltaic' part of photovoltaic cell means it outputs a voltage. otherwise why would it be called that?
 
  • #86
bigbadcityboy said:
surely the 'voltaic' part of photovoltaic cell means it outputs a voltage. otherwise why would it be called that?
Please read up a bit on how photocells and photodiodes work.

And stop calling me Shirley. :rolleyes:
 
  • #87
bigbadcityboy said:
whats an explicit resistor?
It's one that's R-rated. Like the movies.:smile:

Sorry, I'm just getting a little punchy with this long repetitive thread about fairly simple stuff. For the purposes of this thread, just ignore the word explicit.
 
  • #88
i couldn't find any data sheets for solar cells on the digikey thing. I am assumin' itl output something in the mA range
 
  • #89
i always thought u couldn't put an ammeter across a battery, am i wrong?
 
  • #90
help! all my friends say theyr measuring voltage! they say a photovoltaic cell is like a battery so makes voltage not current
 
  • #91
bigbadcityboy,

Photovoltaic cells produce current not a potential difference. May I suggest you read around the subject a little, may I also suggest that you start here; http://en.wikipedia.org/wiki/Photovoltaic_cell.

And you friends will not be measuring voltage unless they are using a current to voltage converter.

~H
 
  • #92
okay, i have read through the thread and firstly i would like to thank hoot and berke for their patience and help. i think it was really unfare (and illegal) of einstein to ask you to write his report for him.

where could i find a type of Light Detector suitable for detecting a infrared source from approx 2 metres away
 
  • #93
super_swifty said:
where could i find a type of Light Detector suitable for detecting a infrared source from approx 2 metres away
What's the application? What's the light source, and its intensity and directivity? How big can the detector be? Can it use light concentration? Are there other interfering IR sources in the same environment? Will you be using modulation/demodulation to reject those other IR sources?

The simplest thing would be to just use an IR remote control transmitter and receiver circuit, along with the IR window for the receiver assembly. You can probably even get them in kit form...
 
  • #94
Hootenanny said:
bigbadcityboy,

Photovoltaic cells produce current not a potential difference. May I suggest you read around the subject a little, may I also suggest that you start here; http://en.wikipedia.org/wiki/Photovoltaic_cell.

And you friends will not be measuring voltage unless they are using a current to voltage converter.

~H
And I'll add that I seem to remember way back somewhere in this thread that the goal was to measure the output of the detector at different distances from the source, in order to figure out how that varies with distance. (Was that this thread?) You can go ahead and measure the output voltage of the photocell, but it's not going to vary much or vary smoothly with distance. When you do a good job of measuring the photocurrent (however you end up doing it), that is when you will get a nice smoothly varying function with respect to the distance from the light source.
 
  • #95
bigbadcityboy said:
Big Up The Physics Masseev Wicked
You talk just like my son! You aren't berkeboy in disguise just messing with me, are you? :rolleyes:
 
  • #96
Would a remote controller for a TV be a suitable infrared source for this experiment? I've edited this because, stupidly, I did not read enough above.
 
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  • #97
Zalaras said:
Would a remote controller for a TV be a suitable infrared source for this experiment? Is there going to be a significant change in the photocell output over the distance of about 1.5 metres?
The IR LED from the transmitter would be a valid source, but you will probably want to force it on instead of leaving it transmitting in code. However, keep in mind that TV remote control receivers use the "current-to-voltage" converter circuitry that hoot and I have alluded to (multiple times), and they have significant gain and AGC and decode circuitry to make it possible to operate over the several meter distances. You're not going to be able to just hook up a DVM in current mode, and see a photocurrent at an IR photodiode from an IR LED a couple meters away.
 
  • #98
bigbadcityboy said:
i always thought u couldn't put an ammeter across a battery, am i wrong?
An ammeter is a short circuit (in reality a low explicit resistance), so hooking it across a voltage source is looking for trouble. You will likely blow the fuse in your ammeter (or DVM's current measuring circuit). And no, you can't borrow my DVM for the experiment.
 
  • #99
Thanks for the info.

I'm in the process of writing up my Scientific Knowledge section and I was wondering if anyone knew of some good sites for information about infrared radiation and photocells in relation to the stated experiment. I've tried some sites but I can't seem to find the type of info I'm looking for.

I have made some predictions based solely on guesses so I really need to check out some more information so I can refine these predictions.

Thanks in advance.
 

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