A2 Physics | Post your doubts here

[optimistic]

@histephenson007 and SkyPilotage! How the hell did you guys prepare for physics. You guys know answers to everything!

 

[angelgirl:)]

@histephenson007 and SkyPilotage! How the hell did you guys prepare for physics. You guys know answers to everything!

lolzzz

 

[worriedman]

How do we know the significant figures/decimal places to give in the answer? Always get them wrong.

 

[histephenson007]

look at the answer here....

hmmm...how come different papers?? there is a different paper in xtremempapers with the same year same name paper!!

 

[smzimran]

How do we know the significant figures/decimal places to give in the question? Always get them wrong.

Give the same number of s.f given in the question
And sometimes, one better s.f

 

[KaiserFury]

Hello,

I have a few questions that I'm hoping you guys can answer asap, as my exam is after tomorrow.

I want to know what to write down as my answer when the question is "What is seen on the screen when electrons are diffracted", first as particles and second as waves. As in, concentric circles and stuff. And why, if possible.

I would also like to know, in AM and FM, how to calculate the carrier frequency and the signal frequency, and how to solve part 10(c) in this paper: http://www.xtremepapers.com/CIE/ind... Level/9702 - Physics/&file=9702_s07_qp_4.pdf

http://www.xtremepapers.com/CIE/ind... Level/9702 - Physics/&file=9702_s08_qp_4.pdf
In number 2, part b(iii) of this paper, the mark scheme says the mass melted by heater in 5 minutes is = 64.7 - 0.5 x 16.6. Why is this? Why isn't it just 64.7 - 16.6?

http://www.xtremepapers.com/CIE/ind...Level/9702 - Physics/&file=9702_s10_qp_42.pdf
I have no idea how to answer number 10(B)

In a reaction, when one nucleus gives off another nucleus and energy, how can the second one be the one having more binding energy if the first one was able to turn to the 2nd one and give off excess energy?

What's the difference between thermionic emission and the photoelectric effect?

I would greatly appreciate any help with my enquiries.

Thank you.

 

[angelgirl:)]

hmmm...how come different papers?? there is a different paper in xtremempapers with the same year same name paper!!

ohhh got r u sure...there r two diff..ms of the same year and ppr?

 

[histephenson007]

How do we know the significant figures/decimal places to give in the answer? Always get them wrong.

Yea, I know how that feels. But they always say they accept 1 extra significant figure. And more good news!! My teacher has attended a conference this year and found out that they are going to be less strict about significant figures from this year. So don't worry, and always use one extra significant figure when in doubt.

 

[histephenson007]

ohhh got r u sure...there r two diff..ms of the same year and ppr?

yea, just check the ms in xtremepapers. something is not right

 

[worriedman]

Different values have different SF in question. Which one should we consider for the SF?

 

[histephenson007]

Different values have different SF in question. Which one should we consider for the SF?

the one with the lowest SF

 

[angelgirl:)]

yea, just check the ms in xtremepapers. something is not right

http://www.xtremepapers.com/papers/...nd AS Level/Physics (9702)/9702_w10_ms_42.pdf
oh yaaaaa look at the answer here...its totally didfferent...

 

[angelgirl:)]

yea, just check the ms in xtremepapers. something is not right

so which 1 is correct according to you?

 

[Jonathan127]

Hi everyone, I'm new here
Could someone please help me with these questions:

October/ November 2005:
http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_w05_qp_4.pdf

Q3 b) (iii) - I don't understand why the increase in internal energy is ∆U = 4.05 × 10^4 – 3050 = 37500 J . Because heat enters the system, so it makes sense that it is positive, but why is the work done on the system negative? I thought that work done by the system is negative.

Q6 c) (ii) I don't understand how to sketch that graph

October/ November 2008:
http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_w08_qp_4.pdf

Q3 b) (ii) - I don't get why a = 11 :S
Q10 b) - I don't understand how the mark scheme has solved this one

May/ June 2009:
http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_s08_qp_4.pdf

Q9 b) - How are we supposed to draw it?



Sorry if these questions have already been asked before. I tried to look through this thread if they had been asked and answered, but I didn't find them.

 

[histephenson007]

so which 1 is correct according to you?

I believe the xtremepapers' paper is the correct one. But I am still trying to find out why the answer is -840J .

 

[angelgirl:)]

I believe the xtremepapers' paper is the correct one. But I am still trying to find out why the answer is -840J .

sure...but thanks alot for this much help...

 

[histephenson007]

sure...but thanks alot for this much help...

GOT IT!!!!!!!!!!

In an earlier question, it asked the total energy change in PQRP which is zero. So, the sum of the third column should be zero. Since we already know that the first two are -360and +720,

-360+720+ x = 0
So, x = -360
Then
u = q + w
-360 = 480 + x
so, x = -360 - 480 = -840

 

[leadingguy]

yay!
But pleaase do help me crack Nov 09 P42 Question 2 c ii)
I cant seem to figure out why this question was omitted.
Plus Im confused of which way to solve it. By charle's law, volume increase hence temperature increases.
But by first law of thermodynamics , work is done by gas hence internal energy decreases, hence kinetic energy decreases so temperature decreases.
This is a bit confusing?

no unable to crack that one bro sorrY

 

[angelgirl:)]

GOT IT!!!!!!!!!!

????

 

[larina]

work done= area of the triangle
1/2 * base * height
work done is P*delta volume
so-----> 1/2* 28*10^8* ((2*10^-4)-(8*10^-4)) {as the arrow is going from R to P}
===> -840J