OCR Physics A2 Planning Exercise

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YorkshirePhoeni
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Hey all!
Not entirely sure if this has been mentioned before but the task in question is to measure the temperature of the glass on a bulb and also the power output for that temperature (basicly the brightness of the bulb) and come up with the maximum possible power output so that the glass temperature is not hot enough to cause danger of burns of fire. I know there will be a number of ways of doing this *using common laboratory equiptment* but i can only think of heating some water using the bulb and calculating the temperature using the specific heat capacity equation. Any other ideas?
Thanks
Luke
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misty
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heya- is this OCR A?
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YorkshirePhoeni
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Yes that would be OCR A, any ideas?
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misty
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heya, you got any further with it yet? we got given it yesterday... so far im thinking immersing the bulb in oil witha thermocouple in and measuring temp V and I and working out poweer.
umm.. dunno about ranges and that yet..
you?
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El Asesino
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I'm stuck on the same, someone told me to use a water calorimeter, so you basically put the bulb into the water until the water and envelope have reached thermal equilibrium but my teacher told me calorimeters measure heat energy and therefore I'm not sure what to use.
What thermometers do you think might be a good idea
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misty
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i thought of a thermocouple
not sure tho. our teacher wont tell us anything
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El Asesino
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Yeah you're right but how do are you going to apply it??
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chats
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I done dat plan 2 weeks ago. most people used a thermocouple the bulb was the 'hot' junction ice was the 'cold junction' the emf across the bulb could give a value of the temp using a calibration chart (finding emf then reading across to get temp) to get the calibration chart u need 2 points using thermocouple i used ice for 0 degrees (no emf) and other side of thermocouple above steam 100 degrees
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El Asesino
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Could you send me a rough copy if you still have one with all the keypoints on it so that you know I won't copy word for word
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3sixty
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I also need a bit of help on this. I understand about the thermo couple and the hot and cold junctions. Just need some information on what to write about in the background bit. Obviously I'd need to write how to calculate power from the voltage etc. and how a thermocouple works... but do I need to write about the heat from the bulb envelope? if so what?

Also, what ranges would you use for the thermocouple?
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kenkennykenken
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Im stuck on this too... :confused:
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misty
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i don tget it- u put one end of thermo coupl ein ice and what w. the other end? would u use the bulb imersed in liquid to get a temp for it?
whats te use of the thermocouple if ur gunna read off temp from a chart using pd? sorry!
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kenkennykenken
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I think the thermocouple measures the difference in pd between the 2 ends? And then from that, you can read off the temperature from the chart...im not really sure. sooo confusing, and theres a word limit of 500 too
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misty
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ah right ok thanks..
we have to give in a kitlist tomorrow so we can have a play w. some apparatus on sat
we write it up on tuesday- how about u?
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kenkennykenken
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You go into school on saturday?

We gotta write it up for the actual practical day (next friday) coz they aren't taking it in till that date. I was gonna write it up like 2 weeks ago, but Ive been putting it off again and again coz i'm stuck with loaaaaaaaads of art to do! I think Im gonna start writing it up this weekend
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misty
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yeh we have sat morning school
we only have a week to look at it then gotta write it under supervised conditions- dammit...hmm i dunno what to do. quite worried... need to talk to some friends methinks!!
heh- im going to bed! nigh tnight x
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kenkennykenken
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Ahh just saturday morning, thats alrite Okie if I find out anything else about the plan I'll post it on here, nite nite
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#18
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When i asked for help bout this planning on this site i got no help at all but i'll try and help u lot. ( i better get sum repuation points for this!)

procedure?
to get calibration graph first just measure emf of two points ice 0 deg= 0 emf steam 100 deg around 4V. so on a graph emf against temp join the two points caus if u do research graph is linear then when u get emf across lamp (furthur on in exp) u can read off temp so a emf of bout 3.5 will be bout 80 deg 2.0V will b bout 50 deg and so on.

why use a thermocouple and not a standard mercury thermometor?
'heat capacity of thermometer is much greater than that of hot juntion of thermocouple, for this reason, the thermocouple is paticuliary useful caus a rapidly varying temp is to be measured. it also covers a larger range of temps'

how to get power?
it isnt just sufficient to take the mark on the light bulb used.
it can be found using P=IV put a voltmeter and ammeter in the circuit and then u can get the power.
then by drawing a graph of power against temp u can show variation.

safety?
u prob all know
but sum are risk of glass breaking,apparatus fallin over, let bulb cool down before touching it.

accuracy?
use crushed ice for cold junction better than ice cubes sumfin to do with surface area.
join thermocouple to hottest part of bulb (top) explain how u know.

F**K this is the longest thread ive ever written!
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misty
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wow thats fantasstic thanks a million..
how did u conect thermocouple to the bulb??
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chats
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(Original post by misty)
wow thats fantasstic thanks a million..
how did u conect thermocouple to the bulb??
u can use insulating tape or just rest the thermocouple on the lamp. the wires are stiff they wont fall off.
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