Physics, Chemistry and Biology: Post your doubts here!

[Nabeel.Ahmad]

Thanks i knew it. But wasn't able to put as the examiner wanted it.

Okay. You're welcome.

 

[eureka!]

I am having problem with moments. Especially stable,neutral and unstable equilibrium..plx help!!!!!!!!!!

Assalamu `alaykum.
Moment is simply the turning effect of a force. When the net force is zero the object attains equilibrium and stability. When a net force greater than zero acts on an object it is said to have unstable equilibrium.
Determining the moment about an object is pretty simple. Moment = force x distance from pivot.
For example, a see-saw. Two kids, each weighing 50 lbs, sit on either end of the see-saw, equidistant from the pivot. The moment is zero. F1 x d1 = F2 x d2, so sum of clockwise moments = sum of anticlockwise moments. However, if one of them sits closer to the pivot than the other, this won't be the case. Remember that in equilibrium, force is always inversely proportional to distance from pivot, as the formula shows.
Now two kids weighing 30 lbs and 20 lbs sit on one side of the see-saw, opposite to a kid weighing 50 lbs. If the see-saw does not turn, the sum of clockwise moments must equal the sum of anticlockwise moments. So F1 x d1 = (F2 x d2) + (F3 x d3).

Hope it helps!

 

[eureka!]

Assalamu `alaykum.
Does the thickness of an object increase when heated, or is it just the length and width?
Nibz gary221

 

[***amd***]

Assalamu `alaykum.
Does the thickness of an object increase when heated, or is it just the length and width?
Nibz gary221

the whole of its volume

 

[princevegeta]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s04_qp_1.pdf
Can somebody help with Q.9 . With explanation ofcourse. greatly appreciate it.

 

[princevegeta]

Anyone?

 

[mohd_one]

princevegeta: Q9 = A = Pb3O4 + 4HNO3 → 2Pb(NO3)2 + PbO2 + 2H2O

____________________________

Can someone please explain Specific Latent Heat and Vaporisation and Specific Heat Capacity along with their subsequent equations? That is the only thing I don't understand in Thermal Physics. And can someone please help me understand sound and light and mention their formulas please?

Thanks. And one last thing, no attachments of notes. Thanks again ^_^

 

[funky brat]

princevegeta: Q9 = A = Pb3O4 + 4HNO3 → 2Pb(NO3)2 + PbO2 + 2H2O

____________________________

Can someone please explain Specific Latent Heat and Vaporisation and Specific Heat Capacity along with their subsequent equations? That is the only thing I don't understand in Thermal Physics. And can someone please help me understand sound and light and mention their formulas please?

Thanks. And one last thing, no attachments of notes. Thanks again ^_^

For this, first you need to know what heat capacity is. Heat capacity is the amount of energy required for a substance to change it's tempeature by 1 degree C. And when you refer to heat capacity, you are always talking about the temperature change with respect to the amount of substance. For example, the heat required for 1g of a substance to change its temperature by 1 degree C is its specicific heat capacity which is denoted by 'c'.
Latent heat of fusion and vapourisation are two different things. The former is used when a solid changes into a liquid or vice versa but latent heat of vapourisation refers to heat during the conversion of a liquid to a gas or a gas to liquid. Latent heat is the 'hidden' heat during which the temperature of the surroundings does not changed infact the energy is utilised in making or breaking of bonds. And the most frequently used formula for claculating the amount of heat provided etc is Q=mc*temperature change.
And I'm not sure if I can explain very well but if you do get it please let me know, I'll elaborate on the other topics as well.

 

[mohd_one]

Ok so specific heat capacity is the amount of energy required to raise the temperature of 1kg of a substance by 1* and the specific latent heat of fusion is the amount of energy needed to change the state of 1kg of a solid to a liq or liq to solid and specific latent heat of fusion is the same but for liq & gases.

For the first one: E = mc(Delta)T
For the second one: (Power*Time)/Mass

Correct?
_____________________________________________________________________________________________________

And for waves:
[*] Transverse Waves are waves that travel perpindicular to the direction of the force. EG: Light
[*] Longtitudinal Waves are waves that travel parallel to the direction of the force. EG: Sound

Electromagnetic spectrum BLABLABLA I already know

[*] Angle i = r
[*] n = sin i/sin r
[*] Air -> Glass (light slows down and bends towards the normal)
[*] Glass -> Air (light speeds up and bends away from the normal)
[*] If sin i = critical angle refraction occurs
[*] If sin i > critical angle (more than) total internal reflection occurs
[*] If sin i < critical angle (bends at 90*)

Then there's the convering lense and convexing lense I which know.

Help with above ^_^

 

[Nabeel.Ahmad]

[*] If sin i = critical angle refraction occurs
[*] If sin i > critical angle (more than) total internal reflection occurs
[*] If sin i < critical angle (bends at 90*)

Then there's the convering lense and convexing lense I which know.

Help with above ^_^

Well, you are not supposed to take the sin of i.

Whenever a ray of light moves from a denser medium to a rare medium, it bends away from the normal, you already know that.
And Why? Because the speed of light increases and the wavelength increases too.

But as you increase the angle of incidence, the angle of refraction increases, in the less dense medium.
There comes an angle when the refracted ray is parallel to the surface. (The angle of refraction is 90*)
The Angle of Incidence for which the angle of refraction in the rare medium is 90 *, that is called the Critical Angle.
Now, if you further increase the angle of incidence, no refraction occurs but the ray is totally internally reflected.

So, you said:

If sin i = critical angle refraction occurs

You don't have to take the sin of i yet. You just have to see if i angle is more than critical angle, less than it, or equal to it.
If it is equal to it, refraction will occur at 90*, parallel to the surface.

If it is less than critical angle, refraction will occur, simply.
But if it is greater than critical angle, then no refraction will occur, but the ray of light will be refracted back inside. This phenomenon is called Total Internal Reflection.

Associated formulas:

n = 1/sin c

 

[funky brat]

Ok so specific heat capacity is the amount of energy required to raise the temperature of 1kg of a substance by 1* and the specific latent heat of fusion is the amount of energy needed to change the state of 1kg of a solid to a liq or liq to solid and specific latent heat of fusion is the same but for liq & gases.

For the first one: E = mc(Delta)T
For the second one: (Power*Time)/Mass

Correct?
_____________________________________________________________________________________________________

And for waves:
[*] Transverse Waves are waves that travel perpindicular to the direction of the force. EG: Light
[*] Longtitudinal Waves are waves that travel parallel to the direction of the force. EG: Sound

Electromagnetic spectrum BLABLABLA I already know

[*] Angle i = r
[*] n = sin i/sin r
[*] Air -> Glass (light slows down and bends towards the normal)
[*] Glass -> Air (light speeds up and bends away from the normal)
[*] If sin i = critical angle refraction occurs
[*] If sin i > critical angle (more than) total internal reflection occurs
[*] If sin i < critical angle (bends at 90*)

Then there's the convering lense and convexing lense I which know.

Help with above ^_^

For the definitions part, you are correct. Sorry, I don't understand which second one are you talking about. If you are asking about the formulas for latent heat of fusion then the formula is L(f)= l(f)*m. Here 'L' represnets the latent heat fo fusion and 'l' for latent heat for fusion and 'm' for mass. This formula is applied to latent heat of vapourisation as well.
As far as the lens are concerned, our syllabus covers only the converging lens (convex) in detail. Please be more specific hwat you do not know about this topic.

 

[Ahmed Qassim]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s12_qp_61.pdf

CHEMISTRY PAPER 6 Q5 HELP NEEDED HOW DO U SOLVE IT PLEASE I HAVE AN EXAM TOMORROW PLEASE HELP FAST!!!!!!!!!!!!!!
HOW DO U DO QUESTIONS SIMILAR LIKE THESE.
Srry but i was absent for school few days and i missed the class about qualitative analysis.Now i read the printed notes but cant understand anything and the teacher wont explain again to me So please help me as far as u can
THX IN ADVANCE

 

[funky brat]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s12_qp_61.pdf

CHEMISTRY PAPER 6 Q5 HELP NEEDED HOW DO U SOLVE IT PLEASE I HAVE AN EXAM TOMORROW PLEASE HELP FAST!!!!!!!!!!!!!!
HOW DO U DO QUESTIONS SIMILAR LIKE THESE.
Srry but i was absent for school few days and i missed the class about qualitative analysis.Now i read the printed notes but cant understand anything and the teacher wont explain again to me So please help me as far as u can
THX IN ADVANCE

To tackle such questions, you need to know the tests for colours and identification of ions and gases thoroughly. If you can get hold of the book by Presscott read the Acids, bases, salts and identification of ions and gases from this book, you'll soon get your doubts clear.
In this question, a carbonate salt is tested. For this you need to know how to test for the presence of carbonate, that is done by adding dilute hcl, since a carbonate is present effervesence occurs (bubbles evolved) and co2 is given off. Now co2 can be identified when it is passed through calcium hydroxide (limewater), it is converted to calcium carbonate therefore turns milky. While the other part of the question is to identify which salt it is. For this you can refer to the information given in part(b) which is that this gas turns moist red litmus paper blue which is the property of alkaline gases. Hence, you can conclude at the end that the salr is ammonium carbonate.

 

[Ahmed Qassim]

Thx man u are a life saver

 

[mohd_one]

Tests for Gases:

GasFormulaTests
Ammonia NH3 Turns damp red litmus paper blue
Carbon dioxide CO2 Turns limewater milky
Oxygen O2 Relights a glowing splint
Hydrogen H2 ‘Pops’ with a lighted splint
Chlorine Cl2 Bleaches damp litmus paper
Nitrogen dioxide NO2 Turns damp blue litmus paper red
Sulfur dioxide SO2 Turns acidified aqueous potassium dichromate(VI) from orange to green

Tests for Anions:

AnionTestResult
Carbonate (CO32-) Add dilute acid Effervescence,
carbon dioxide produced

Chloride (Cl-)
(in solution) Acidify with dilute nitric acid, then add
aqueous silver nitrate White ppt.
Iodide (I-)
(in solution) Acidify with dilute nitric acid, then add
aqueous silver nitrate Yellow ppt.
Nitrate (NO3-)
(in solution) Add aqueous sodium hydroxide, then
aluminium foil; warm carefully Ammonia produced
Sulfate (SO42-) Acidify, then add aqueous barium nitrate White ppt.

Tests for aqueous cations:

CationEffect of aqueous sodium hydroxideEffect of aqueous ammonia
Aluminium (Al3+) White ppt., soluble in excess giving a
colourless solution White ppt., insoluble in excess
Ammonium (NH4+) Ammonia produced on warming –
Calcium (Ca2+) White ppt., insoluble in excess No ppt. or very slight white ppt.
Copper (Cu2+) Light blue ppt., insoluble in excess Light blue ppt., soluble in excess,
giving a dark blue solution
Iron(II) (Fe2+) Green ppt., insoluble in excess Green ppt., insoluble in excess
Iron(III) (Fe3+) Red-brown ppt., insoluble in excess Red-brown ppt., insoluble in excess
Zinc (Zn2+) White ppt., soluble in excess,
giving a colourless solution White ppt., soluble in excess,
giving a colourless solution

 

[Ahmed Qassim]

Tests for Gases:

GasFormulaTests
Ammonia NH3 Turns damp red litmus paper blue
Carbon dioxide CO2 Turns limewater milky
Oxygen O2 Relights a glowing splint
Hydrogen H2 ‘Pops’ with a lighted splint
Chlorine Cl2 Bleaches damp litmus paper
Nitrogen dioxide NO2 Turns damp blue litmus paper red
Sulfur dioxide SO2 Turns acidified aqueous potassium dichromate(VI) from orange to green

Tests for Anions:

AnionTestResult
Carbonate (CO32-) Add dilute acid Effervescence,
carbon dioxide produced

Chloride (Cl-)
(in solution) Acidify with dilute nitric acid, then add
aqueous silver nitrate White ppt.
Iodide (I-)
(in solution) Acidify with dilute nitric acid, then add
aqueous silver nitrate Yellow ppt.
Nitrate (NO3-)
(in solution) Add aqueous sodium hydroxide, then
aluminium foil; warm carefully Ammonia produced
Sulfate (SO42-) Acidify, then add aqueous barium nitrate White ppt.

Tests for aqueous cations:

CationEffect of aqueous sodium hydroxideEffect of aqueous ammonia
Aluminium (Al3+) White ppt., soluble in excess giving a
colourless solution White ppt., insoluble in excess
Ammonium (NH4+) Ammonia produced on warming –
Calcium (Ca2+) White ppt., insoluble in excess No ppt. or very slight white ppt.
Copper (Cu2+) Light blue ppt., insoluble in excess Light blue ppt., soluble in excess,
giving a dark blue solution
Iron(II) (Fe2+) Green ppt., insoluble in excess Green ppt., insoluble in excess
Iron(III) (Fe3+) Red-brown ppt., insoluble in excess Red-brown ppt., insoluble in excess
Zinc (Zn2+) White ppt., soluble in excess,
giving a colourless solution White ppt., soluble in excess,
giving a colourless solution

THX MAN
THANK U ALL FOR THE HELP

 

[OmgiTheNinja]

Umm can someone help explain to me, how you can perform the dependency of certain variables for photosynthesis after destartching? Because don't the cells in the leaves die when boiled?

 

[black widow]

Umm can someone help explain to me, how you can perform the dependency of certain variables for photosynthesis after destartching? Because don't the cells in the leaves die when boiled?

i think u are confusing destarching with 'killing' the leaf'
destarching involves placing the plant in a dark place for 48 hours so that the plant uses up all its starch without making more glucose. The cells in the leaf are still alive and there is chlorophyl to produce glucose in sunlight
killing involves placing the leaf in boiling water to break down the cell walls of the lead and kill the leaf cells (mesophyll cells), then placing it in ethanol (to extract the chlorophyll), and then to place it in warm water to make it brittle. as a result, the leaf cannot photosynthesize even when placed in sunlight

now as for the experiment to investigate the dependancy of certain variables for photosynthesis, we must know the conditions for photosynthesis
The conditions for photosynthesis are
-Light
-Chlorophyll
-Water
-Temperature
-CO2

Change one factor at a time and keep the others constant. The results of the experiment will acknowledge u the dependancy of each of the variables

 

[Allah's Slave]

A box of 40 kg is being pushed up a 2.0m inclined plane. What is the work done by the 250N force when the box reaches the top of the inclined plane which is 1.0m above the ground?

I've applied the formula Work done=force x distance and got 500J (which is right), but i was thinking that the formula W=mgh could be applied as the plane is inclined and there is some height" and gravitational potential energy and so by this formula i got 400J (which appearently is wrong) , so how can i distinguish between these formulas??? and why isn't W=mgh the right one?

Can we use calculator in Physics Extended 0625?

 

[black widow]

A box of 40 kg is being pushed up a 2.0m inclined plane. What is the work done by the 250N force when the box reaches the top of the inclined plane which is 1.0m above the ground?

I've applied the formula Work done=force x distance and got 500J (which is right), but i was thinking that the formula W=mgh could be applied as the plane is inclined and there is some height" and gravitational potential energy and so by this formula i got 400J (which appearently is wrong) , so how can i distinguish between these formulas??? and why isn't W=mgh the right one?

Can we use calculator in Physics Extended 0625?

the question says
what is the WORK DONE by the 250N force...

when the question says what is the WORK DONE, then use the formula
w=force x dis5ance

when the question says what is the GRAVITATIONAL POTENTIAL ENERGY of the object, then u use the formula
w=mgh