Physics, Chemistry and Biology: Post your doubts here!

[ahmedish]

in 0625_s12_qp_31.pdf 11)b) i know which components to use but idk which should be in which gap. its supposedly a resistor in gap A and LDR in gap B. can someone show me how the current will be flowing so i can understand why its in gap B?
I understand that at night the resistance increases so the voltage increases.

 

[Mohammed Kamel]

does anyone have the marking scheme for bioogy from 1993to 2003 please

 

[idklol]

Biology:

Are the lungs an example of homeostasis (maintaining oxygen levels in blood via. diffusion)

 

[♣♠ Magnanimous ♣♠]

Biology:

Are the lungs an example of homeostasis (maintaining oxygen levels in blood via. diffusion)

Yes -->
The respiratory system -- which comprises the nose, the mouth, the lungs and several other organs involved in breathing -- is involved in various important aspects of homeostasis.
The respiratory system participates in a variety of homeostatic processes, and the two most important of these are maintaining pH and regulating gas exchange. Both of these homeostatic functions are related to the biochemical roles played by the two primary respiratory gases, carbon dioxide and oxygen. Oxygen enters the body as a component of the air we breathe and is processed by the lungs. Carbon dioxide, which is produced as a byproduct of cellular metabolism, travels through the bloodstream to the lungs and is exhaled.

 

[phyo phyo]

ev


i did that too but the mark scheme says you have to subtract it from the first answer. i do not understand why

If the ball is released from that height, without giving initial energy by the player, the kinetic gained by the ball will be only 5.4 J, which is mgh=0.6 x 10 x 0.9. But now kinetic energy gained is 14.7 J. So player must give initial energy of 9.3 J ( 14.7 - 5.4).

 

[ShailB]

Hey guys, I have a question for the science exams:
Suppose we write an answer, but it isn't in the marking scheme, but it isn't wrong either. Would the examiners go strictly by the marking scheme or use their fair judgement as well?

 

[fire wall]

Someone please help me solve q3 and q1 b in may/june /61/2012
my exam is tommorrrow
write down the explanation of graphs or snipping tool screen shots

 

[fire wall]

someone please solve q3 and 1b may/june/2012/61
write explanation or snipping tool screen shots for diagram and drawing my exam is tommorow early morning

 

[Atharva Joshi]

How long does it take to prepare thoroughly for Physics, Chemistry and Biology, with atleast 10 years of past papers practice?

 

[Sofia Kamla619]

Biology:

Are the lungs an example of homeostasis (maintaining oxygen levels in blood via. diffusion)

what did you write for question number 5? I was confident about my answer,but not so sure anymore.

 

[fire wall]

help me with this working and explanation of this question ANYONE HERE

 

[Lucy Black]

can someone help me wid dis..

 

[Lucy Black]

and dis...

 

[ShailB]

can someone help me wid dis..

200cm3 of oxygen, which is in excess. After the reaction, 40cm3 of oxygen remains. SO the total amount of oxygen used would be 160cm3. 100cm3 of CO2 would be used, as it is given,and 20cm3 of hydrocarbon. Rearrange this set up:
20cm3 of hydrocarbon + 160cm3 of oxygen ---> 100cm3 of CO2 + xcm3 of water.
all are in cm3 and all are multiple of each other, so just divide by 20cm3
hydrocarbon+8O2 ---> 5CO2 + xH2O
To find the hydrocarbon, you need the C first. And you take that from the CO2. There are 5Cs
So it will be a pent-
there are 16 oxygens on the left side, and so far, 10 oxygens in the CO2, so the remaining oxygens in H2O would be 6. So it would be 6H2O
Now you know how many Hs there are too (12)
So the formula of the hydrocarbon is: C5H12

 

[Lucy Black]

200cm3 of oxygen, which is in excess. After the reaction, 40cm3 of oxygen remains. SO the total amount of oxygen used would be 160cm3. 100cm3 of CO2 would be used, as it is given,and 20cm3 of hydrocarbon. Rearrange this set up:
20cm3 of hydrocarbon + 160cm3 of oxygen ---> 100cm3 of CO2 + xcm3 of water.
all are in cm3 and all are multiple of each other, so just divide by 20cm3
hydrocarbon+8O2 ---> 5CO2 + xH2O
To find the hydrocarbon, you need the C first. And you take that from the CO2. There are 5Cs
So it will be a pent-
there are 16 oxygens on the left side, and so far, 10 oxygens in the CO2, so the remaining oxygens in H2O would be 6. So it would be 6H2O
Now you know how many Hs there are too (12)
So the formula of the hydrocarbon is: C5H12

thnxx...
can u help me wid d next too

 

[ShailB]

and dis...

use the moles concentration formula.
# of moles= (concentration/1000)*volume
so.
0.2/1000*100 so you would get 0.02 as the number of moles.
then you use the other moles formula: # of moles = mass/molar mass
so
0.02= x/170
so x = 170*0.02
which is, 3.4

 

[Lucy Black]

use the moles concentration formula.
# of moles= (concentration/1000)*volume
so.
0.2/1000*100 so you would get 0.02 as the number of moles.
then you use the other moles formula: # of moles = mass/molar mass
so
0.02= x/170
so x = 170*0.02
which is, 3.4

thnxxx...got it...

 

[fire wall]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w11_qp_32.pdfj
just 6 c
explanation
working please

 

[ShailB]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w11_qp_32.pdfj
just 6 c
explanation
working please

Alright then
so you know the moles formula: # of moles = mass/molar mass
so you got 1.398/233 which is 0.006
now the same number of moles are used for the MgSo4 which is hydrates, as given in the equation, so 0.006 for that too
the mass of one mole is basically the molar mass. you rearrange the formula, to get 1.476/0.006 to get 246g
and then they tell you that MgS04 alone is 120. So now you subtract to leave behind the mass of water, which is 246-120 which is 126
and then you divide by the molar mass of water to get the number of moles which is basically 126/18 to get 7

 

[Taha Ahmed Baig]

Marrkscheme of Biology from year 1993-2003 paper 1,3,and6 plzz i need it