[Physics] Mistakes in the 2009 Specimen Paper Mark Scheme?

[Eyas]

I've seen a few:

Question B1, Part 2, (a)

In the question, we are given a ratio of areas. According to the syllabus itself, the magnification is a ratio of lengths, so when calculating the magnification, one must take the square root of the ratio (taking the square root was omitted from the mark scheme). If we take the square root, the indentations of the leaf will actually be resolved. The question should either refer to the lengths of the leaves or the values of the areas must change so that the question is correct.

Question B2, Part 1, © (i)

The mark scheme says:

number of atoms in 1 kg of carbon =12 x 1000 / N_A

number in 1 kg of U-235 = 235 x 1000 / N_A

If that was the case, 1 kg of carbon would contain 0.2 * 10^-20 atoms! Which is of course untrue. Same applies for the number in 1 kg of U-235.

The ACTUAL number of atoms in 1 kg is given by:

for C-12: 1/(12u)

for U-235: 1/(235u)

Thus the final answer of the ratio will be 2.3 * 10^6

[diabolicalangle]

wouldnt the actual number of atoms be:

for 1kg U-235

(N_A/ 235) * 1000?

and likewise for 1 kg C-12

(N_A/12) * 1000

[Eyas]

wouldnt the actual number of atoms be:

for 1kg U-235

(N_A/ 235) * 1000?

and likewise for 1 kg C-12

(N_A/12) * 1000

Correct. 1/(235*u) and 1/(12*u) would also work, though.

[diabolicalangle]

kk. well im glad thats over

[sweetnsimple786]

I know this is a bit irrelevant, but how do you convert between u and MeV/c^2 ?

I spent about 8 minutes trying to work the conversion and then just BS'ed it.

[diabolicalangle]

off the top of my head, i think its 1 u = 931.5 MeV / c^2.

im pretty sure its in the constant part of the data booklet.

EDIT: yea, i was right.

Edited May 13, 2009 by diabolicalangle

[Tilia]

I did an old paper which had a question in the manner "deduce that the acceleration is this much" and one of the data values given was incorrect (77 x 10^3 instead of 7.7 x 10^3). Would you get full marks on that question regardless of if you used the given wrong data and hence got the wrong answer or if you realized that they had forgotten the . and got the right answer?

[sweetnsimple786]

I'm not too experienced in IB exams (I've only taken a couple so far), but I would use the 77*10x^3 if it was a free-response question and I would note on the lines that the data didn't match up or something like that. If it was multiple choice, then I would use the 7.7*10^3.

Edited May 24, 2009 by sweetnsimple786

[Tilia]

OK. It was a paper 2, but it was so obvious that they had made a mistake... Anyway, hope there aren't any mistakes in the M10 exams.