OCR Physics B - G491 (Physics in Action) January 2012

For the resistance question, you had to look at the graph first to find the voltage at that temperature then use V=IR to find the current flowing through the circuit. As the current is constant through a series circuit and the total emf equals the sum of the voltage across each component you could sub in the values. The answer was around 497 Ohms I think if I didn't make any mistakes. Hope that helps.

EDIT: don't quote me on that, I might have made a mistake but i can't remember the question.

(edited 12 years ago)

Reply 21

Apocalyptic Fish

OP

1

Original post by Jordy2212

Hey, Yeh I also found it went well, but I did find the resistance question and the tennis ball question tricky. The resistance question said there was 6V across the fixed resistor which confused me, as the EMF was 6V?? I ended up getting 500 Ohms for the answer.

Also for the final questions about the comparison of ceramics and plastics, did you get for the first part because plastic would melt under the high temperature in the lamp, and for the 2nd because plastics are much more ductile??

Hopefully A boundary around 42/60 :smile:

Yeah, I can't remember what resistance I put, it was probably wrong anyway. For the last question I said ceramics are highly resistant to heat and the 2nd one I said plastics are better insulators and ceramics may break if used for a plug.

Reply 22

Matt G

Original post by Jordy2212

Hey, Yeh I also found it went well, but I did find the resistance question and the tennis ball question tricky. The resistance question said there was 6V across the fixed resistor which confused me, as the EMF was 6V?? I ended up getting 500 Ohms for the answer.

Also for the final questions about the comparison of ceramics and plastics, did you get for the first part because plastic would melt under the high temperature in the lamp, and for the 2nd because plastics are much more ductile??

Hopefully A boundary around 42/60 :smile:

I put for the first one that ceramics have stronger bonding so are more resistant to heat than plastics and would not melt in the halogen lamp. For the second, I said that ceramics are brittle and may break under general wear and tear while plastics are tougher.

Reply 23

anonymouspie227

20

i got around 500 Ohms for the resistance one

Reply 24

KING2011BOB

Anyone remember any more of the harder variety of questions?
When it said work out the extension when the stress is 1.1 gpa does that mean you use the strain worked out previously-I do think it does?

Reply 25

KING2011BOB

My biggest complaint to ocr would be the spacing between questions there were no places to put your workings really,maybe I just have large handwriting-some of teh writing ones had a reasonable amount but for the equations ones,I found I had to use like both sides of the page!

Reply 26

anonymouspie227

20

Original post by KING2011BOB

My biggest complaint to ocr would be the spacing between questions there were no places to put your workings really,maybe I just have large handwriting-some of teh writing ones had a reasonable amount but for the equations ones,I found I had to use like both sides of the page!

I think there was a moderate amount of space.., but in some it was a bit tight, but if they made larger spaces- people may think they reqquire a lot more working out than necessarily needed? lol and get confuzzled.

Reply 27

KING2011BOB

Original post by ChunkyFudgeLover101

I think there was a moderate amount of space.., but in some it was a bit tight, but if they made larger spaces- people may think they reqquire a lot more working out than necessarily needed? lol and get confuzzled.

Yeah I think thats exactly right

Reply 28

Jordy2212

What did you all get for the sensitivity of the graph?

Reply 29

KING2011BOB

Original post by Jordy2212

What did you all get for the sensitivity of the graph?

0.3v per degrees I do think thats wrong but I dunno tbh

Reply 30

Joel R

7

Original post by Jordy2212

Hey, Yeh I also found it went well, but I did find the resistance question and the tennis ball question tricky. The resistance question said there was 6V across the fixed resistor which confused me, as the EMF was 6V?? I ended up getting 500 Ohms for the answer.

Initially confused me as well, then I re-read it: it actually said that the p.d. across the potential divider was 6V...essentially just re-iterating that there was no internal resistance in the cell.

I put D because of the largest %.

Hope that's right...that's what I changed mine to after remembering a past exam question that was very similar :smile:

Reply 31

TamsynJoll

For the Sensitivity, I just calculated delta Y/ delta x.
Therefore, in this case, the Change in Voltage divided by the Change in Temperature at 70 degrees. Hoping that's right!

Reply 32

Joel R

7

I calculated the gradient using two squares on the x-axis (4 degrees) either side of seventy. I think it was 0.4/8=0.05 V per degree in the end?

Reply 33

geraghty

see for the one of the first questions to match what linked to what?

Reply 34

TamsynJoll

Original post by Joel R

I calculated the gradient using two squares on the x-axis (4 degrees) either side of seventy. I think it was 0.4/8=0.05 V per degree in the end?

Mine was similar, However I drew a line across horizontally at 70 degrees, to whatever that value was. So therefore my 'delta y' was 'that estimated value MINUS where the line began on the y axis' then divided that by 70 degrees MINUS 0.

Reply 35

Joel R

7

Original post by TamsynJoll

Mine was similar, However I drew a line across horizontally at 70 degrees, to whatever that value was. So therefore my 'delta y' was 'that estimated value MINUS where the line began on the y axis' then divided that by 70 degrees MINUS 0.

Wouldn't that give you the average sensitivity below 70 degrees, rather than the actual sensitivity at 70?

Reply 36

TamsynJoll

Ah well.. It's all done now. :L :P

Reply 37

Apocalyptic Fish

OP

1

Original post by KING2011BOB

See for the EMF q you had to use the graph to find what voltage you get at 70 degrees-3.7 v so you need 2.3 v across the other resistor
The 800=69% of the voltage so I did 800/69 * 39 = 511 ohms

I think around 41-42 marks for an A is reasonable for this paper tbh