OCR Physics A G484 - The Newtonian World - 11th June 2015 Watch

Oraeng
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Hi guys, would appreciate some help with this question (from OCR textbook):

The oven of a domestic cooker has a volume of 0.1 m^3. The pressure in the oven is 1 atmosphere 1x10^5 Pa.
At constant atmospheric pressure the density of the air at 227 degrees C is x times the density of the air at 27 degrees C. Calculate the value of x.

Don't understand it - how can the pressure and volume of the air be constant if the temperature has risen?
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Raizel
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(Original post by MathsAddict)
How is everyone's revision going i find g484 easier than g482 tbh. Haven't really touched g485 since like 2 weeks ago.
yeah i agree man, alot of g484 questions are basically (here are some numbers and here is this paper you have with some letters, put the numbers in the letters)
g482 is harder I think. hopefully g485 questions are as nice, I wouldn't know because I haven't done a full g485 paper yet, had too many exams this year, hard to juggle them all.
spent most of my time working on c3 c4.
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MathsAddict
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(Original post by Oraeng)
Hi guys, would appreciate some help with this question (from OCR textbook):

The oven of a domestic cooker has a volume of 0.1 m^3. The pressure in the oven is 1 atmosphere 1x10^5 Pa.
At constant atmospheric pressure the density of the air at 227 degrees C is x times the density of the air at 27 degrees C. Calculate the value of x.

Don't understand it - how can the pressure and volume of the air be constant if the temperature has risen?
I would have thought that x would be 5/3. is that the answer?
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MathsAddict
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(Original post by Raizel)
yeah i agree man, alot of g484 questions are basically (here are some numbers and here is this paper you have with some letters, put the numbers in the letters)
g482 is harder I think. hopefully g485 questions are as nice, I wouldn't know because I haven't done a full g485 paper yet, had too many exams this year, hard to juggle them all.
Same and also its the fact that for some reason my maths module m1 helps with all the suvat and forces. I still have 6 exams to go and just done 4 this week. So i hope to juggle and try to remember as many things as possible.
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Chung224
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G484 is by far my worst exam....their mark schemes are absolute bullcrap
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sagar448
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(Original post by Chung224)
G484 is by far my worst exam....their mark schemes are absolute bullcrap
That and the grade boundaries for an A* is terrible..
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issy_246
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Hi guys I need help on doing this question as I find it really difficult, could someone please post an answer on this question so I could see how you worked it out in each step. I need to know how to do I would appreciate it if anyone could.
Thanks(urgently)
q1)Pyrometers are used to measure the temperature of substancesremotely where direct measurement is not practical or possible. One suchexample is measuring the temperature of blast furnaces in steel making. Theyuse Stefan’s Law to calculate the temperature based on the amount of energyreceived. If the amount of energy received by the pyrometer is 7.01x105Wm-2calculate the temperature of the furnace in °C. Stefan’s Constant, σ, = 5.7x10-8Wm-2K-4.
q2)
  1. Blast furnaces are made from steel andlined with refractory bricks to keep as much heat energy in and to prevent thefurnace from melting. If the temperature within the furnace is as above, thethermal conductivity of the refractory brick is 1.4, the thermal conductivityof the steel is 43, the thickness of the protective brick lining is 1m, thethickness of the steel casing is 500mm, and the energy transferred through bothlayers is as above, calculate the temperature at the boundary of the lining andthe casing if the outside temperature of the blast furnace is 50°C.
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Oraeng
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(Original post by MathsAddict)
I would have thought that x would be 5/3. is that the answer?
No answer is 3/5. Could you explain please?
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Oraeng
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(Original post by sagar448)
That and the grade boundaries for an A* is terrible..
How do you find out A* grade boundaries?
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MathsAddict
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(Original post by Oraeng)
No answer is 3/5. Could you explain please?
The question wants the ratio of 227 degrees to 27 degres. You need to work with thermodynamic unit of kelvin for this.

So 27 degrees = 273+27= 300
and 227 degrees = 273+227=500

Then to work out the ratio for x do 300/500 which should be the answer. I misread it and did it backwards my bad XD
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MathsAddict
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(Original post by Oraeng)
How do you find out A* grade boundaries?
You need A in AS 240 points then you need uniform 270 points in A2 for an A* which doesn't make sense tbh
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Oraeng
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(Original post by MathsAddict)
The question wants the ratio of 227 degrees to 27 degres. You need to work with thermodynamic unit of kelvin for this.

So 27 degrees = 273+27= 300
and 227 degrees = 273+227=500

Then to work out the ratio for x do 300/500 which should be the answer. I misread it and did it backwards my bad XD
Of course thanks, completely forgot about converting to kelvin duhhh

(Original post by MathsAddict)
You need A in AS 240 points then you need uniform 270 points in A2 for an A* which doesn't make sense tbh
What I was really asking was is there any way to find out A* grade boundaries for individual exams as I thought this was what you were referring to. I'm guessing we can just scale it from the A grade boundary?
Also why do you think it doesn't make sense? Seems like a perfectly fine way of doing it to me.
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MathsAddict
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(Original post by issy_246)
Hi guys I need help on doing this question as I find it really difficult, could someone please post an answer on this question so I could see how you worked it out in each step. I need to know how to do I would appreciate it if anyone could.
Thanks(urgently)
q1)Pyrometers are used to measure the temperature of substancesremotely where direct measurement is not practical or possible. One suchexample is measuring the temperature of blast furnaces in steel making. Theyuse Stefan’s Law to calculate the temperature based on the amount of energyreceived. If the amount of energy received by the pyrometer is 7.01x105Wm-2calculate the temperature of the furnace in °C. Stefan’s Constant, σ, = 5.7x10-8Wm-2K-4.
q2)
  1. Blast furnaces are made from steel andlined with refractory bricks to keep as much heat energy in and to prevent thefurnace from melting. If the temperature within the furnace is as above, thethermal conductivity of the refractory brick is 1.4, the thermal conductivityof the steel is 43, the thickness of the protective brick lining is 1m, thethickness of the steel casing is 500mm, and the energy transferred through bothlayers is as above, calculate the temperature at the boundary of the lining andthe casing if the outside temperature of the blast furnace is 50°C.
First use the information of the stefan's constant to get a kelvin of some sort would be my apporach so i wold do 7.01x10-5x5.7x10-8= 0.04 rounded up and the units would be K-4 since i just cancelled the other two units. But hold up can i see the original question? to double check what i done on my paper is correct. i got 296K rounded up?
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sagar448
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(Original post by Oraeng)
Of course thanks, completely forgot about converting to kelvin duhhh



What I was really asking was is there any way to find out A* grade boundaries for individual exams as I thought this was what you were referring to. I'm guessing we can just scale it from the A grade boundary?
Also why do you think it doesn't make sense? Seems like a perfectly fine way of doing it to me.
For individual exams, just find the difference between the A grade and the B grade and add it to the A grade.
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MathsAddict
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(Original post by Oraeng)
Of course thanks, completely forgot about converting to kelvin duhhh



What I was really asking was is there any way to find out A* grade boundaries for individual exams as I thought this was what you were referring to. I'm guessing we can just scale it from the A grade boundary?
Also why do you think it doesn't make sense? Seems like a perfectly fine way of doing it to me.
Hmm tbh i prefer g485 unit over g482. But my teacher messed up my AS coursework i got a b and then i got a high b in unit 1 so i cant get an A in AS unless i pull of 140/150 in g482 which would i doubt i got.
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Oraeng
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(Original post by MathsAddict)
Hmm tbh i prefer g485 unit over g482. But my teacher messed up my AS coursework i got a b and then i got a high b in unit 1 so i cant get an A in AS unless i pull of 140/150 in g482 which would i doubt i got.
Awh that sucks. I hated G482 last year I definitely prefer G485, just managed to scrape an A in it and flunked G481 and my practicals so ended up getting a B in AS too. Resat my practicals and G481 and I'm fairly confident I've pulled it up to an A (fingers crossed!). Did you not resit G481?
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MathsAddict
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(Original post by Oraeng)
Awh that sucks. I hated G482 last year I definitely prefer G485, just managed to scrape an A in it and flunked G481 and my practicals so ended up getting a B in AS too. Resat my practicals and G481 and I'm fairly confident I've pulled it up to an A (fingers crossed!). Did you not resit G481?
Well done though props to you on g482 and hopefully you ate g481 alive.
i didnt see a point seeing i had 10 exams anyway so i left it as it was and resat g482 hopefully pulled off a comfortable A. Then this year i need to smack g484 and g485 and my coursework should be solid as it was monitored by like 3 different people.
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Oraeng
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(Original post by MathsAddict)
Well done though props to you on g482 and hopefully you ate g481 alive.
i didnt see a point seeing i had 10 exams anyway so i left it as it was and resat g482 hopefully pulled off a comfortable A. Then this year i need to smack g484 and g485 and my coursework should be solid as it was monitored by like 3 different people.
Haha I'm hoping so - found g481 childs play after doing so much mechanics this year! Yeah fair enough, good luck to you!
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MathsAddict
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(Original post by Oraeng)
Haha I'm hoping so - found g481 childs play after doing so much mechanics this year! Yeah fair enough, good luck to you!
True my friends suggested i did it as it would require virtually no revision except a little bit. But i was content that i would avenge myself in the other modules. Do you also do maths?
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Oraeng
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(Original post by MathsAddict)
True my friends suggested i did it as it would require virtually no revision except a little bit. But i was content that i would avenge myself in the other modules. Do you also do maths?
Yep and further maths. Doing M1 and M2 so along with G481 and G484 I feel like a mechanics wizard this year Definitely a good thing since I'm gonna be doing engineering at uni! Guessing you do maths too hence the username?
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