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# OCR Physics AS Planning Exercise watch

1. use a metre rule. cos its slidin doors their not gonna want measurements exact to a few milimetres or watever.
wat sorta circuit diagrams are u lot usin????
2. (Original post by whirlwind)
why shouldn't we use a photovoltaic photocell?
exactly! you cant use a photovoltaic cell because it will not detect waves with wavelengths above 700nm! and obviously, the wavelength of infra-red is around 850 (i think)... so you can't use a photovoltic cell... all this time, i was on the wrong track and i got to change my plan again (which shouldn't be a problem i guess...)
3. You have to use equipment available in the average science school science lab. Dont get too hung up on the photocell or the IR emitter.
4. What can I include in the background information section? Can I just say some stuff about infrared waves and leave it there or should I actually go in detail about the automatic doors and how infrared radiation is used in order for it to work?
5. (Original post by Coolraj)
What can I include in the background information section? Can I just say some stuff about infrared waves and leave it there or should I actually go in detail about the automatic doors and how infrared radiation is used in order for it to work?
Im gonna put in some info about different types of photocells and infrared detectors. how many words r we supposed 2 use??? We could put in other uses for photodiodes. i dunno im sooo confused
6. 500 word limit. You dont have room for that kind of stuff.
7. ok... its due in tomorrow and here i am...
this might sound crazy but I only got 3 steps for the experiment...
1. connect the circuit according to the diagram
2. change the distance and record the voltmeter reading in a table
3. display the data in a graph, draw best line fit and find its gradient...
does it sounds fine? i mean... theres something missing... (of course, I did expand on those points but even then...) has anyone else got any more idea?
8. (Original post by Coolraj)
ok... its due in tomorrow and here i am...
this might sound crazy but I only got 3 steps for the experiment...
1. connect the circuit according to the diagram
2. change the distance and record the voltmeter reading in a table
3. display the data in a graph, draw best line fit and find its gradient...
does it sounds fine? i mean... theres something missing... (of course, I did expand on those points but even then...) has anyone else got any more idea?
have you put stuff like zero readings and repeats in?

Mine has to be done tomorrow (well, today now) aswell. I've got nine steps in the method, but there's not much more than what I'm guessing you have... it's pretty simple, really.
9. 500 words!! Don't get caught up in going into detail about crap! Also you should probably want to use a metre rule because why would you want a screwgate micrometer or a gps to measure the size of a door? Make this something that is easy for the examiner to mark so he/she can just tick off your marks- bullet points and annotated diagrams may prove useful!
Of course you can mention a little about different types of photocells and infrared detectors eg "i will use a photodiode instead of an LDR because photodiodes are much more sensitive to infra-red light" but try to keep it as short as that; it is incredibly easy to go off on a tangent and write lots of in-depth physics and end up writing 1000 words!
10. 500 words!! Don't get caught up in going into detail about crap! Also you should probably want to use a metre rule because why would you want a screwgate micrometer or a gps to measure the size of a door?
11. Oops..... Double post; had trouble with the editing option
12. oh! thats good... tnx for helping me out...
13. ok so im going to have a photocell in series with a resistor and im going to mesure the pd( voltage) of the resistor. ok this is really stuid question but im confused. when the photocell receives more light its resistance drops so does that mean that the pd across the resistor will increase?
so my graph or voltage agaisnt distance will have a negative gradient?

meterrule! lol you could probably get away with a 20cm one i dont think your equiptment is gonna be able to measure further than a distance of 10cm between the light source and the photocell. college equipment isnt exactly great.
14. Think of the order of magnitude of a typical door... 20cm?
15. dude you're not actually doing the experiment you are doing a scaled down version! like you equipment in college is actually capable of doing a realistic experiment seeing as an automatic door is like 2m+ wide! the equipment you are using will probably not even be able to travel a metre. i mean what kind of light source are you using? and IrLED? from college i mean its not exactly the strongest!
plus you didnt even answer my question
anyways care to say what your real name is? i know you got to ensfc :P
16. (Original post by w00t)
when the photocell receives more light its resistance drops so does that mean that the pd across the resistor will increase?
so my graph or voltage agaisnt distance will have a negative gradient?
Yes, should do.
17. w00t my plan is fine then XD no need to stress phew!
18. by the way guys... I think you have to work out the size of the resistor... I have just been told that...
19. Yeah you have to i guess since you will need one in the circuit diagram.
20. all you have to do is search photocell on google the first hit gives you good values for a resistor

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