Biology; Chemistry; Physics: Post your doubts here!

[Awesome12]

What is the process of Crystallisation ? How is it used as a purification technique ? I don't understand this topic :/ Please help

Well basically, crystallization involves taking a solution and heating it, and the leaving it to cool. For example, you have a solution of sugar and water, and you need to get the sugar from the water. If you heat it, all of the water will evaporate, but so will the sugar. When you leave it to cool, sugar molecules join back together to form crystals of sugar. Well, basically the concept here is that the first crystals to appear are always the purest

 

[asadalam]

Well basically, crystallization involves taking a solution and heating it, and the leaving it to cool. For example, you have a solution of sugar and water, and you need to get the sugar from the water. If you heat it, all of the water will evaporate, but so will the sugar. When you leave it to cool, sugar molecules join back together to form crystals of sugar. Well, basically the concept here is that the first crystals to appear are always the purest

Abhi tak inhi kamon mai
I'm so tensed for the result,less than 3 weeks away D:

 

[Awesome12]

Abhi tak inhi kamon mai
I'm so tensed for the result,less than 3 weeks away D:

lol. I just answered 2 questions ever since the exams ended.
Who isn't?

 

[Bhaijan]

A question from 5054_w02_qp1 (physics)
The answer is D. B should allow more evaporation, hence more coolness. Very confusing

 

[amazingphysics1]

A question from 5054_w02_qp1 (physics)
The answer is D. B should allow more evaporation, hence more coolness. Very confusing





View attachment 46180

The Answer would be A, as the liquid in the can which has the fastest heat loss to surrounding via radiation of heat as well as evaporation, would be at the lowest temperature. For this Can A is the answer as it hasa dull black surface which losses heat by radiation the fastest, coupled with the fact that it does not have a lid, hence rate of evaporation is also high as compared to option C & D. After some time, the "hypothetic" temperatures of all the cans would be A = 60, B = 65, C =70 & D =75. (www.faraz4physics.com)

 

[Mohame Areeh]

The answer is A. Skim this http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_w02_er.pdf . And by the way evaporation will only cool the cans at high temp, because the high enrgetic molecules escapes, leaving the low energetic ones.

 

[Mohame Areeh]

The answer is A. Skim this http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_w02_er.pdf . And by the way evaporation will only cool the cans at high temp, because the high enrgetic molecules escapes, leaving the low energetic ones.
The answer is A. Skim this http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_w02_er.pdf . And by the way evaporation will only cool the cans at high temp, because the high enrgetic molecules escapes, leaving the low energetic ones.

 

[Mohame Areeh]

29 Each of the diagrams below is a cross-section through two parallel current-carrying conductors.
Which diagram correctly shows the magnetic field pattern formed by the currents in the two
conductors?

30 A wire hangs between the poles of a magnet.
When there is a current in the wire, in which direction does the wire move?

please say why it was the ans. it is from may/june physicc (5040)

 

[Bhaijan]

A Question 5054_w05_qp 1 , i don't really understand this question at all!!!

 

[Bhaijan]

Another question 5054_w05_qp1

 

[Awesome12]

A Question 5054_w05_qp 1 , i don't really understand this question at all!!!
View attachment 46294

The answer is D
For current to flow, there must be a complete circuit. Since the birds are not touching the ground, current won't flow through their body.

Another question 5054_w05_qp1
View attachment 46295

1 - Pay attention to the question. It mentions a hot LIQUID. This means it is not gaseous.
2 - The graph displayed is a cooling curve

A - Boiling and Evaporation?

===> No we are not heating it


B - Condensation?

===> No there is no gas involved, we are dealing with a hot LIQUID


C - Evaporation?

===> Evaporation does occur at all times, but there is something else happening that explains the change of state


D - Solidification and Evaporation

====> Evaporation occurs at all temperatures. Solidification explains the change in state


ANSWER = D

 

[asadalam]

The answer is D
For current to flow, there must be a complete circuit. Since the birds are not touching the ground, current won't flow through their body.



1 - Pay attention to the question. It mentions a hot LIQUID. This means it is not gaseous.
2 - The graph displayed is a cooling curve

A - Boiling and Evaporation?

===> No we are not heating it


B - Condensation?

===> No there is no gas involved, we are dealing with a hot LIQUID


C - Evaporation?

===> Evaporation does occur at all times, but there is something else happening that explains the change of state


D - Solidification and Evaporation

====> Evaporation occurs at all temperatures. Solidification explains the change in state


ANSWER = D

10 days left.....

 

[Bhaijan]

A question from Physics that's confusing.
The answer is C, but I am confused between the two choices C and D. Of course there is a concept involved here which at this point I haven't fully grasped

 

[Bhaijan]

29 Each of the diagrams below is a cross-section through two parallel current-carrying conductors.
Which diagram correctly shows the magnetic field pattern formed by the currents in the two
conductors?
View attachment 46220
30 A wire hangs between the poles of a magnet.
When there is a current in the wire, in which direction does the wire move?
View attachment 46219
please say why it was the ans. it is from may/june physicc (5040)

The Answer for the second question is A using Fleming's Left Hand Rule.
The Answer for the first question is C, using Right Hand Grip rule we can work out the direction of the magnetic field in the wires.
After this we come to the conclusion that the magnetic fields would repel each other, because of them being in the same direction.
For better understanding study the image below:

 

[Dark Destination]

A question from Physics that's confusing.
The answer is C, but I am confused between the two choices C and D. Of course there is a concept involved here which at this point I haven't fully grasped
View attachment 46332

The gas supply exerts a greater pressure than the atmosphere.. as seen from the top manometer..
The water on the left side of the u-tube is lower.. the same should be the case if the liquid is replaced with mercury.
D is impossible, and easily the option that people realize is not the answer for sure..

 

[Dark Destination]

10 days left.....

7 days now. ._.

 

[asadalam]

7 days now. ._.

I'm actually not dreading it too much,just get it over with already...its such a long wait......

 

[Mohame Areeh]

thx

 

[Mishellin Maisha]

I want to know about the concept of metal wire becoming live and fuse blowing. MCQ section has really confusing questions related to this. I just do not understand the main concept. The issue of earth wire is also confusing. There are also problems about potential dividers in which the voltage might even go to 0. This is all quite confusing

 

[mohamed kamal]

HELP .......................

In paper 23 November 2013 for math (CIE) - Question no. 16 a
Area in triangle in mark scheme is multiplied by pie !
It should be = 0.5 x 3 x 3 x sin 120 ... only !