Physics, Chemistry and Biology: Post your doubts here!

[Razo513]

I feel soo stupid
anyway thx alot

on the contrary u shouldn't! , i explained it like the teacher did .... not my thinking

 

[JOEJOE]

OLD BIO PP?????

 

[Moar]

OLD BIO PP?????

Here is paper 1 : http://www.freeexampapers.com/get_past_papers.php?l=Past_Papers/IGCSE/Biology/CIE/1993 - 2003/Questions Paper 1 June 1994 -- 2004.pdf
Here is paper 3: http://www.freeexampapers.com/get_p...+2003/Questions+Paper+3+June+1993+--+2004.pdf
and paper6 : http://www.freeexampapers.com/get_p...+2003/Questions+Paper+6+June+1993+--+2004.pdf
I wish they start putting oldies here on xtremepapersfor people like you

 

[sweetiepie]

hope this helps evryone

 

[suhaib05]

http://www.xtremepapers.com/CIE/Cambridge IGCSE/0625 - Physics/0625_w10_qp_33.pdf
I'm not sure what I'm supposed to do for question 10(a). Can someone please upload an image showing the answers to parts (i) and (ii)?

 

[GlitteringLights]

It takes 2 hours to heat up 280 000 cm
3
of water from 20 °C to 50 °C. The density of
water is 1000kg/m
3
.
Calculate the specific heating capacity of water.
State the formula that you use and show your working.
formula used
working

time-2 hrs
volume= 280,000c^3
density= 1000 kg/m
temp change= 50-20=30 degrees
c= ?
power= >> should have been given o.o

the formula is : E=mc x delta T
ie
energy= mass x specific heat capacity x temp change

1) to find mass, we use the formula
density = mass/volume
mass= densityx voulume
(dont forget convert to same units )
mass=1000kg/m x (280,000/1000,000)
mass= 280 kg

2) energy= power x time

therefore we substitute that into the formula
pt=mc x delta T

double check the question, i think they gave the value of power somewhere
3) then you just substitute the values

 

[GlitteringLights]

oh sorry, the power is 5KW....
So how would you enter that into pt=mc x delta Temp?
..to get the S.H.C

thankyou

yeah see

given values:
time=2 hrs x 60 x 60 (convert to SI unit > seconds)
volume= 280,000cm^3= 0.28 m^3 (SI unit)
density= 1000 kg/m^3
temp change= 50-20=30 degrees
power= 5kW
c= ?

i explained how to find mass above
now we need to find energy
or directly substitute

so the formula was:
pt=mc x delta T
5kW x (2 x 60 x 60 ) = 280 x c x 30
36,000 = 8,400 c
c =4.29

[PS: just check the answer,, incase i made a mistake in converting to SI units kay and let me know if i did ]

 

[GlitteringLights]

THANK YOU!! The answer says: "4290" But I guess it's right ,right? Anyway thanks alot and if you want to add something to your answer please do.Greetings

yes ! i found my mistake, i forgot to convert the power to SI unit as well :$
so basically it is 5000 x 2 x 60 x 60 = 8,400 c
c= 36,000,000/8400
c=4285.7
c=4290
(i had also rounded it previously to 4.29 form 4.2857)

anndd you're welcome

 

[Moar]

Help in physics paper 1 october 2003, question 21.
Why is it A and not C ?
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_w03_qp_1.pdf

 

[GlitteringLights]

Help in physics paper 1 october 2003, question 21.
Why is it A and not C ?
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_w03_qp_1.pdf

because the distance between A and the wavefront is less than that with C
the question says, waves travel slower where the water is shallow, the wave near c has traveled a huge distance and A the least
therefore answer is A

 

[Moar]

because the distance between A and the wavefront is less than that with C
the question says, waves travel slower where the water is shallow, the wave near c has traveled a huge distance and A the least
therefore answer is A

Makes sense, thx alot

 

[GlitteringLights]

Makes sense, thx alot

haha no problem

 

[Moar]

Physics paper 1 doubt... again
In physics papar 1 june 2011, question 22
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_s11_qp_11.pdf
Why is it D, i mean the image might be magnified if the lens got close, so it won't be inverted. I thought A should be the right answer...

 

[Moar]

So it's important to decide that it's a real image. Remeber that real images are ALWAYS INVERTED

Real images are those where the light rays acually converge,whereas virtual images are locations from where the light appears to have converged.
(Real images are created when the object is placed outside the focal length of the converging lens/mirror)
The question also says "which statement is ALWAYS correct"
So as you see in the question the image is inverted which tells you that it is a real image so you can conclude that it will STAY INVERTED (a real image will not suddenly become a virtual image )
ANd without complicating anything I'll just say that ,yest, the image can get bigger or smaller than the object but it will always be inverted .
Just remember that, you will only be expected to know covex(converging) lenses anyway.

Well i am still a little confused :S . I mean he said that the lens and the screen are moved , so wouldn't the focal length change and then the object might be between principal focus and the centre.
Or you are assuming that because both the screen and the lens are moved so there is no overal change?

 

[GlitteringLights]

Physics paper 1 doubt... again
In physics papar 1 june 2011, question 22
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_s11_qp_11.pdf
Why is it D, i mean the image might be magnified if the lens got close, so it won't be inverted. I thought A should be the right answer...

>it's not A because the principle focus is the point where the RAYS converge. an image isn't normally formed here

>it's not B because the screen and the lens are moved and the size of n image depends on the distance between the lens and the object and changes wit the position

>it's not C because again the screen and the lens are moved so the distance changes with the positioning

>therefore the answer is D (firstly because it can't be any other option =P , and secondly because real images are always inverted)
*remember only real images can be reproduced or displayed on a screen unlike virtual images
i hope its clear now

 

[Moar]

Thank you both !! i guess because it is a real image that is shown , and a virtual image wouldn't be displayed on the screen, therefore when checking the answers i should exclude virtual image.
Correct me if i am wrong

 

[adilahmed900]

Hi guys.
Can some one help me out here?
I didn't take any tuition of Biology, Chemistry and Physics.
Now I am having trouble, where should I study all the lab experiments and investigations from which are in the GCE O level course????
Like the colour changes etc? Can any one help me out please? Should I just do the ATP papers? OR is there any specific place where there are notes to study for chemistry biology physics colour changes, lab activities and investigations?? HELP HELP ??

 

[suhaib05]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w09_qp_32.pdf
Question 4c (ii): How am I supposed to know that the third product is sulphur dioxide? Thanks in advance!

http://www.xtremepapers.com/CIE/Cambridge IGCSE/0625 - Physics/0625_w10_qp_33.pdf
I'm not sure what I'm supposed to do for question 10(a). Can someone please upload an image showing the answers to parts (i) and (ii)?

Just a reminder that this is still unanswered...

 

[999]

Does anyone have old past paper 3s for chemistry. Like the 1996,1997.........2000?

 

[wooowooowoo]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w09_qp_32.pdf
Question 4c (ii): How am I supposed to know that the third product is sulphur dioxide? Thanks in advance!
.

(CH3)2 S
If we expand the group, it becomes.. C2H6. C2H6 is a hydrocarbon (Alkane) and upon decomposition of alkane, they give away Carbon Dioxide and Water.
Then we are left with S. So, S + O2 -> SO2