Biology; Chemistry; Physics: Post your doubts here!

[usama321]

1 mol Mg-----1 mol H2
(24 g) -----24 dm3 H2
0.036 g --------------x
x=24*0.036/24=0.036dm3 H2 is produced with 24 g Mg

actually this is the normal procedure. Your teacher might have just told you this so that you may learn it more easily. But it's always better to understand the concept behind it. 0.036/24 =0.0015g is Mass/Ar, which is the formula to get the number of moles of a substance. Next, as one mole occupies 24dm3, 0.0015 would occupy 0.0015*24= 0.036dm3 of volume.

 

[Saad Mughal]

1 mol Mg-----1 mol H2
(24 g) -----24 dm3 H2
0.036 g --------------x
x=24*0.036/24=0.036dm3 H2 is produced with 0.036 g Mg

actually this is the normal procedure. Your teacher might have just told you this so that you may learn it more easily. But it's always better to understand the concept behind it. 0.036/24 =0.0015g is Mass/Ar, which is the formula to get the number of moles of a substance. Next, as one mole occupies 24dm3, 0.0015 would occupy 0.0015*24= 0.036dm3 of volume.

I do it with the formulas.

 

[usama321]

I do it with the formulas.

what formulas?

 

[Saad Mughal]

what formulas?

Moles = Mass (g)/Ar or Mr.
Volume = Moles * Molar Gas Volume.

 

[fatima0000]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s08_qp_2.pdf
Q no 4) part (b)
how to solve it????

 

[usama321]

energy for oxygen = 200* 1.7*9 = 3060 J
energy for nitrogen = 800*2**9 = 1440 J
total = 1440 + 3060 = 17460 J

 

[TheStallion-Reborn]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s08_qp_2.pdf q3 part b i knw all about convection convention and radiation....but hw to do this damn question??

 

[Saad Mughal]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s08_qp_2.pdf q3 part b i knw all about convection convention and radiation....but hw to do this damn question??

*conduction.
The shiny foil blanket traps air b/w the skin and the blanket (air being a good insulator) prevents the skin from conducting heat to the surroundings.
The blanket prevents the air from flowing to and from the skin, this reduces the effects of any convectional currents (breezes in surroundings).
The shiny blanket is a reflector of radiation so any heat loss is prevented and reflected by the shiny foil.
3 points - 3 marks.

 

[Hskk]

You all must be aware of these formulae: 1) Power=VI 2) P=I2R 3) P=V2/R
In the second formula power and resistance is directly proportional while in the third they both are inversely proportional?
Also, on what factor does the brightness of a lamp depend?

 

[TheStallion-Reborn]

What is the difference between real image and virtual image??

 

[usama321]

You all must be aware of these formulae: 1) Power=VI 2) P=I2R 3) P=V2/R
In the second formula power and resistance is directly proportional while in the third they both are inversely proportional?
Also, on what factor does the brightness of a lamp depend?

i think it depends on the power, that is both the voltage and current, but i am not sure.

What is the difference between real image and virtual image??

real image is the one formed on the other side of the lens than the object. Virtual is formed at the same side of the lens as the object.

 

[Hskk]

What is the difference between real image and virtual image??

A real image can be formed on a screen but a virtual image can not be.

 

[Hskk]

i think it depends on the power, that is both the voltage and current, but i am not sure.


real image is the one formed on the other side of the lens than the object. Virtual is formed at the same side of the lens as the object.

What will your answer be to N03/P1/Q25?

 

[Saad Mughal]

What is the difference between real image and virtual image??

Real image can be projected on a screen (for example a projector, camera). It is formed behind the mirror/lens.
A virtual image cannot be projected (used in spotlights). It is formed on the same side as the object.

 

[Saad Mughal]

What will your answer be to N03/P1/Q25?

"The filament of lamp X is thicker and shorter than that of lamp Y".
The answer is B. R=l/A, X is thicker and shorter (hence has lesser resistance than Y) which means Y has the larger resistance.
X will be brighter because V=IR, when the resistance is lower, the current is higher (since the voltage is same from the mains).

 

[usama321]

What will your answer be to N03/P1/Q25?

mine would be B

 

[fatima0000]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s08_qp_2.pdf
Q no 11 (a) (i)

 

[Hskk]

"The filament of lamp X is thicker and shorter than that of lamp Y".
The answer is B. R=l/A, X is thicker and shorter (hence has lesser resistance than Y) which means Y has the larger resistance.
X will be brighter because V=IR, when the resistance is lower, the current is higher (since the voltage is same from the mains).

Physics Matters pg 374. One of the reasons of choosing tungsten as the filament's metal in a lamp is its high resistivity. Higher resistance = higher temperature thus more light generated. According to the book, Y should be brighter.

 

[TheStallion-Reborn]

RADIOACTIVITY!
In a magnetic field, the beta particles are deflectd more than the alpha particles because they are lighter. But s marking scheme states, the deflection of radioactive particles between two opositly charged plates is due to the the attraction and repulsion from both the plates. So does that mean that here alpha particles will be deflected more because they have a greater charge of +2 as compared to -1 of the beta particles.

 

[TheStallion-Reborn]

i guess there is a mistake in a markhing scheme... for this paper http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s12_qp_21.pdf question 11 part b sub part 2, the marking scheme http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s12_ms_21.pdf says DOWN towards POSITIVE plate. whereas the positive plate is on top. is it really a mistake or is it supposed to be this way?