Physics, Chemistry and Biology: Post your doubts here!

[sj0007]

Can anyone tell me how to draw the reflection of circular wavefronts? like in question 10 of the paper: w10 qp 33
Thnx.................

 

[masterex567]

Can someone please help me out on this.!
Q6 a) i) and ii)... can u please explain with reasons.! Thanks in advance.!

Q6 a) i) is Range.
Range is the difference between highest and lowest temperature,
now if you increase the stem of the thermometer you'll have a larger difference between highest and lowest hence a bigger range.

Q6 a) ii) is Sensitivity.
Sensitivity is how much the liquid expands per rise in temperature.
If you want it to react more per temperature rise, decreasing diameter of the capillary tube to make it thin, will make the liquid rise up more according to scale.
Hence if diameter reduced, liquid will seem to expand more per degree rise.

 

[masterex567]

Can anyone tell me how to draw the reflection of circular wavefronts? like in question 10 of the paper: w10 qp 33
Thnx.................

1. First you need to find the dot R (Q10 a i) which is the same distance from surface on other side as S is.
2. Now put your compass on S, and complete the three circles to the other side of the surface.
3. Now place your compass on R, and try to complete a circle from the circular wavefronts drawn on the right hand side to make a circle on this left hand side.
4. Repeat instruction in 3, to complete circles from right hand side to left hand side, from compass on R for all three wavefronts.
5. After its drawn, erase the circles on right hand side of reflecting surface leaving ones drawn on the left hand side.

There you go, ask if you need any clarification with above.

 

[Saad the Paki]

Q6 a) i) is Range.
Range is the difference between highest and lowest temperature,
now if you increase the stem of the thermometer you'll have a larger difference between highest and lowest hence a bigger range.

Q6 a) ii) is Sensitivity.
Sensitivity is how much the liquid expands per rise in temperature.
If you want it to react more per temperature rise, decreasing diameter of the capillary tube to make it thin, will make the liquid rise up more according to scale.
Hence if diameter reduced, liquid will seem to expand more per degree rise.

U rock man.. thanks alot..!

 

[Saad the Paki]

W

1. First you need to find the dot R (Q10 a i) which is the same distance from surface on other side as S is.
2. Now put your compass on S, and complete the three circles to the other side of the surface.
3. Now place your compass on R, and try to complete a circle from the circular wavefronts drawn on the right hand side to make a circle on this left hand side.
4. Repeat instruction in 3, to complete circles from right hand side to left hand side, from compass on R for all three wavefronts.
5. After its drawn, erase the circles on right hand side of reflecting surface leaving ones drawn on the left hand side.

There you go, ask if you need any clarification with above.

Wouldnt R be on the surface because that is the source of the reflected waves..?! :/

 

[sohaib ul haq]

Cao + Sio2 = CaSio3


why no water formed
as

acid + base = salt + water

 

[sohaib ul haq]

and can u ppl tel me a easy way of finding which reaction is exo or endo

and how many past exam paper should be done for A*

 

[masterex567]

W

Wouldnt R be on the surface because that is the source of the reflected waves..?! :/

It's on the other side, as the question asks where it "SEEMS" to come from.

 

[sohaib ul haq]

Cao + Sio2 = CaSio3


why no water formed
as

acid + base = salt + water


and can u ppl tel me a easy way of finding which reaction is exo or endo

and how many past exam paper should be done for A*


some one help me out plz

 

[masterex567]

Cao + Sio2 = CaSio3


why no water formed
as

acid + base = salt + water


and can u ppl tel me a easy way of finding which reaction is exo or endo

and how many past exam paper should be done for A*


some one help me out plz

It is formed but Calcium Silicate (CaSiO3) has "high physical water absorption",
so calcium silicate is basically hydrated in nature and absorbs the water hence no water is produced as end result in reaction.

If its taking in heat its endo, you can identify if the reaction needs heat to complete and thus will be endo.
Also, sometimes they give the heat values in delta H. If the value is negative, that means the reaction is exothermic.

In my opinion, do structured to gain an understanding of how to answer the questions. Then do multiple choice to develop reasoning.
But go through the textbooks to ensure you know everything, since sciences rely on reasoning and past paper questions won't repeat.

- If i made any mistake in the above explanation, please let me know.

 

[sohaib ul haq]

reactivity series (of metals n hydrogen is wat u need in d IGCSEs) :
please
stop
calling
me
a
crazy
zombie
if
that
large
hippo
can't
swim
gug glug!
plug plug!
first letter of each word denotes d first letter of each metal in order <_<

plz --- k
send ----Na
littel ---- li lithium
chat ---- Ca
massala ---- Mg
and ---- Al
chota --- C - Carbon
zebra ---- Zn
if ----Fe - iron
the ----Sn - tin
horse ---- H
cant ---Cu
make ----Mn - manganise
sweet ----Ag -silver
goldish ----Au -gold
poop ----Pt -platnium

 

[sohaib ul haq]

ans is B


but it can also be C
explain plz



and can anyone tell the reason why stainless steal dont rusts

 

[masterex567]

ans is B


but it can also be C
explain plz



and can anyone tell the reason why stainless steal dont rusts

It can't be C, because if it is less finely powdered, the granules are larger and hence occupy a SMALL surface area.
Rate of reaction decreases with surface area, hence the answer cannot be C.

Also stainless steel doesn't rust because apart from 70% iron, it contains 20% chromium, and 10% nickel I think.
These compounds (Chromium and Nickel) help protect the iron (sacrificial protection) from rusting since they react with the water and oxygen to form a protective oxide layer like in aluminium

Cheers

 

[sohaib ul haq]

It can't be C, because if it is less finely powdered, the granules are larger and hence occupy a SMALL surface area.
Rate of reaction decreases with surface area, hence the answer cannot be C.

Also stainless steel doesn't rust because apart from 70% iron, it contains 20% chromium, and 10% nickel I think.
These compounds (Chromium and Nickel) help protect the iron (sacrificial protection) from rusting since they react with the water and oxygen to form a protective oxide layer like in aluminium

Cheers

thankz man ur best

 

[sohaib ul haq]

plz explain

• volume relation with rate
• volume relation with concentration

 

[sohaib ul haq]

the second point in the increases the surface area so why ans is B

explanation plz

 

[Saad the Paki]

the second point in the increases the surface area so why ans is B

explanation plz

It says SIZE is increasing.. not surface area.. they are 2 different things..
Size means the lumps or granules are getting bigger instead of smaller (crushed) so surface area is decreasing

 

[sohaib ul haq]

Q ) which metal is best for overheated cable

Q ) plz explain :

• volume relation with rate
• volume relation with concentration

 

[sohaib ul haq]

0625/32/M/J/11


Q3) a(1) explain why it is necessary to keep total volume the same in all the experiments ?


can anyone give exlpanation to the answer in the markscheem

 

[masterex567]

0625/32/M/J/11


Q3) a(1) explain why it is necessary to keep total volume the same in all the experiments ?


can anyone give exlpanation to the answer in the markscheem

I can't find this question in the paper you mentioned. Q3) a(1) is about moments in this paper, please link the paper here?