Physics, Chemistry and Biology: Post your doubts here!

[Khadu33]

Guys, question from physics CIE 0625/31/O/N/2008 , 5(c)(i)
Using a 40W heater, 16.3 g of ice is melted in 2.0 minutes. The heater is then switched off. In a further 2.0 minutes, 2.1 g of ice is melted.
Calculate the value of the specific latent heat of fusion of ice from these results.

40W x 2min will gv energy then less the masses and apply the formular L=ENERGY divide by mass

 

[Hanzalla]

Sorry?
But if the coil is horizontal ,so the magnetic field lines are also horizontal,Then how are they cut then?

Its like when a tyre is pushed down a cliff, when it reaches the bottom of the cliff, It will have the greatest Kinetic Energy even though there is no steep road ahead of it . Same goes for the coil. You can assume that tyre on the bottom of the cliff is Coil at horizontal position. OMG I cant convey what I want to make you understand xD

 

[Aayan Muttaqi]

40W x 2min will gv energy then less the masses and apply the formular L=ENERGY divide by mass

Yes but the thing is why do they subtract 2.1 g from 16.3 g ? I need an explanation for this. How is 2.1 g related to 16 .3 g?

 

[Khadu33]

Yes but the thing is why do they subtract 2.1 g from 16.3 g ? I need an explanation for this. How is 2.1 g related to 16 .3 g?

fusion is the change of state from solid to liquid due to this energy is released to the surrounding as the temp remain constant

 

[Aayan Muttaqi]

I must be really dumb to not get this. 16.3 g of ice melted due to the energy supplied from the heater. It was switched off , 2 minutes later 2.1 g of ice melted (correct me if I am wrong, the 2.1 g of ice melted due to energy from the surroundings, right?). I do understand that the latent heat of fusion of ice does not increase the ice's temperature, rather it only changes its state. My question is why are we subtracting 2.1 g from 16.3 g? Or is it because 2.1 g of the ice is a part of the 16.3 g of the ice?

 

[Ayesha Asif333]

Ive done the refraction,reflection and diversion experiments,But ive never seen a ray box.
So that means it doesn't come in Paper 4??

Dispersion*
..how did u do the experiments? What was your light source if not the ray box ?
Yes, thats exactly what it means

 

[Ayesha Asif333]

Guys, question from physics CIE 0625/31/O/N/2008 , 5(c)(i)
Using a 40W heater, 16.3 g of ice is melted in 2.0 minutes. The heater is then switched off. In a further 2.0 minutes, 2.1 g of ice is melted.
Calculate the value of the specific latent heat of fusion of ice from these results.

Lf= Q /m
The energy used to melt the ice here is P *t ....which is 40 * 120 ...time converted into sec
Once u get ure energy divide it by the mass melted which is 16.3
40*120/ 16.3

 

[Ayesha Asif333]

guys need ur help >why would a brass key not sink if its attached on a wood?

Sink in what?
The total density of the brass and the wood will become lower than the density of what ever liquid...thus float

 

[Ayesha Asif333]

Sorry?
But if the coil is horizontal ,so the magnetic field lines are also horizontal,Then how are they cut then?

I assume ure talking about the simple ac generator, the picture in the book that shows a coil looped into a rectanglar shape in between the two poles of the strong magnet
And they have also given the diagram of the cycle of turns ...voltage is 1 when side ab and cd are in the magnetic field, r perpendicular to the field lines here...they cut them but as side ab moves upwards ....it moves along the magnetic field so voltage is 0
I am looking for a better explanation to give u...or maybe someone can explain ...but i hope it gets cleared

 

[Aayan Muttaqi]

Lf= Q /m
The energy used to melt the ice here is P *t ....which is 40 * 120 ...time converted into sec
Once u get ure energy divide it by the mass melted which is 16.3
40*120/ 16.3

No, it will give you the wrong answer. The correct answer is (40*120)/(16.3-2.1) = 338.

 

[Adeen Atif]

Its like when a tyre is pushed down a cliff, when it reaches the bottom of the cliff, It will have the greatest Kinetic Energy even though there is no steep road ahead of it . Same goes for the coil. You can assume that tyre on the bottom of the cliff is Coil at horizontal position. OMG I cant convey what I want to make you understand xD

Haha ,Thanks!
I understood now.
And the way you explained was awesome Tbh.

 

[Adeen Atif]

I assume ure talking about the simple ac generator, the picture in the book that shows a coil looped into a rectanglar shape in between the two poles of the strong magnet
And they have also given the diagram of the cycle of turns ...voltage is 1 when side ab and cd are in the magnetic field, r perpendicular to the field lines here...they cut them but as side ab moves upwards ....it moves along the magnetic field so voltage is 0
I am looking for a better explanation to give u...or maybe someone can explain ...but i hope it gets cleared

Thank you!
I understand it now

 

[Adeen Atif]

Dispersion*
..how did u do the experiments? What was your light source if not the ray box ?
Yes, thats exactly what it means

The good o'l sunlight.
What can I say,my school really was an expert at finding alternatives

 

[Adeen Atif]

Guys!
If Im correct, I may not be the only one bored of the dark font of this website (no offense to dark colors,I actually love em) I mean Cmon its kindof less practical.
So I decided to make a Google plus community where we can discuss almost everything that we discuss here.+ There we can share pictures,PDFs and everything much more easily and its theme is quite simple and practical as well.
So it would be really cool if you join the community https://plus.google.com/u/0/communities/109947941374570116120

 

[Ayesha Asif333]

No, it will give you the wrong answer. The correct answer is (40*120)/(16.3-2.1) = 338.

Can't be
either the question they gave is wrong or the mark scheme is wrong, it has to be a mistake and yes the examiners r humans so can make
what happens to water after the heating has stopped and in further two mins is not required
the head examiner says something else in the report, he says to subtract it with 21 something
They r prolly trying to make a fool out of us

 

[Ayesha Asif333]

Thank you!
I understand it now

Anytime

 

[Khadu33]

I must be really dumb to not get this. 16.3 g of ice melted due to the energy supplied from the heater. It was switched off , 2 minutes later 2.1 g of ice melted (correct me if I am wrong, the 2.1 g of ice melted due to energy from the surroundings, right?). I do understand that the latent heat of fusion of ice does not increase the ice's temperature, rather it only changes its state. My question is why are we subtracting 2.1 g from 16.3 g? Or is it because 2.1 g of the ice is a part of the 16.3 g of the ice?

Aayan Muttaqi see will the weight of an ice and weight of water be the same? no ryt because wen its in solid form the force that holds the ice particles are strong and due to the lattice arrangement make the weight of the ice heavy n wen the change of state takes place the mass decreases coz that force of attraction btewn particle are less stronger than in ice state also energy is absorded to break the bond coz of that the mass also decreases hope am correct guy plz contribute n help this guy if there is a better ans thank you

 

[Ayesha Asif333]

My question is why are we subtracting 2.1 g from 16.3 g? Or is it because 2.1 g of the ice is a part of the 16.3 g of the ice?

i find no reason
if we subtracted 2.1 from 18.4 ( total) that would have made sense
if the 16.3g of ice melted in 4 mins then the subtraction would have made sense
and the did tell us 16.3g has melted in two mins so y reduced it to 14.2? it would contradict the first line of the ques itself
so i said earlier divide the energy with 16.3 and not 14.2

 

[Ayesha Asif333]

Aayan Muttaqi see will the weight of an ice and weight of water be the same? no ryt because wen its in solid form the force that holds the ice particles are strong and due to the lattice arrangement make the weight of the ice heavy n wen the change of state takes place the mass decreases coz that force of attraction btewn particle are less stronger than in ice state also energy is absorded to break the bond coz of that the mass also decreases hope am correct guy plz contribute n help this guy if there is a better ans thank you

yes but y r we subtracting the masses

 

[Khadu33]

yes but y r we subtracting the masses

we want to find the mass that was took part in fusion only thats y we subtract