Physics, Chemistry and Biology: Post your doubts here!

Sijal Mirza

Sijal Mirza

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can u please tell me what topics from physics come in the ATP paper? (O-level) like in chemistry its mainly just Acids, Bases n Salts , Rate of reaction and Moles..
PLEASE HELP!
 
Princess Raven

Princess Raven

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Lockedin said:
they absorb more heat energy from the hot water
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hey i have a question in chemistry.. do u know y copper cannot react with a dilute acid to form a salt?? i mean y do we have to change it to copperoxide or copperchloride?? plz reply ASAP
 
CaveDweller65

CaveDweller65

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Princess Raven said:
hey i have a question in chemistry.. do u know y copper cannot react with a dilute acid to form a salt?? i mean y do we have to change it to copperoxide or copperchloride?? plz reply ASAP
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Copper is quite low in the reactivity series
It's oxide or chloride is perhaps more reactive!
 
gary221

gary221

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Princess Raven said:
So its not just gonna be copper then right... i mean if they say silver or platnium the same rule applies?? and what if they are really high in the reactivity series? would we be able to make a salt?
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yes, includes all non reactive metals.
n u will gt a salt ----> metal + acid = salt + hydrogen.
 
Mariam879

Mariam879

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I facing a serious problem with paper 1 chemistry for some reason , any advice / tips/or anything to help me improve?
 
gary221

gary221

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mak kings said:
Hey..ud any1 me in PHY PA.PA ............. Q11b in mj - p31 -2010 ...plz.plz1 !! any 1 ..i realy cnt understand it!!
http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Physics (0625)/0625_s10_qp_31.pdf
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We know that R = ρL/A
Since the diameter of the second wire(d2) is half the diameter of the first wire (d1), the area of the second wire(A2) is one fourth the area of the first wire(A1)
[as area = pi * (d/2)^2 ie pi *r^2]
So, R2 = (0.45/0.3) * R1
ρL2/(A1/4) = (0.45/0.3) * (ρL1/A1)
on solving, the two ρ n the A1 cancel each other out.
We get, 4L2 = 1.5 * L1
L2 = (1.5/4) * L1
L2 = 0.375 * L1
L2 = 37.5 % of L1
Hope u gt it!!
:p
 
CaveDweller65

CaveDweller65

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Princess Raven said:
So its not just gonna be copper then right... i mean if they say silver or platnium the same rule applies?? and what if they are really high in the reactivity series? would we be able to make a salt?
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Yes, the same rule applies with noble metals such as Platinum,Silver,Gold or those quite low in the reactivity series!
If they are high in the series, yes u can definitely prepare a salt, However metals such as Sodium and Potassium will result in a Very Dangerous Reaction!
Only M.A.Z.I.T metals (Magnesium, Aluminum, Zinc, Iron, Tin) are most suitable! (y)
 
GorgeousEyes

GorgeousEyes

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Could anybody explain to me why when we use step up transformer the current is reduced so we use thinner and lighter cable ? i can't get what the relation between the current and the cables.
 
gary221

gary221

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GorgeousEyes said:
Could anybody explain to me why when we use step up transformer the current is reduced so we use thinner and lighter cable ? i can't get what the relation between the current and the cables.
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the larger the current, the larger the heat losses.
since the current is reduced, thinner wires can be used, as the heat produced will be much less... so thin wires will not be melted.
 
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