A2 Physics | Post your doubts here

[leadingguy]

for same substances the latent heat of vaporisation is greater then the latent heat of fusion.
esplain why??

 

[JohnChemistry]

for same substances the latent heat of vaporisation is greater then the latent heat of fusion.
esplain why??

As you heat a solid turning it into a liquid, you increase the kinetic energy of its molecules, moving them further apart until the forces of attraction are reduced to allow it to flow freely. Keep in mind the forces of attraction still exists. Now as you heat a liquid, turning it into a gas, the kinetic energy of the molecules are increased to a point where there are no forces of attraction between the molecules.
The energy required to completely separate the molecules, moving from liquid to gas, is much greater that if you were just to reduce their separation, solid to liquid. Hence the reason why the latent heat of vaporization is greater that the latent heat of fusion.
Some confusion arrises from the idea that temperature is a measure of the average kinetic energy of a system, and since the temperature remains constant, the average kinetic energy must also remain constant.
The extra energy required to cause a phase transition is actually potential energy. It is the energy required to overcome the bonds of nearest neighbors to the point that a phase transition can occur. So it really isn't a change in kinetic energy.

But for the exam as long as you know that in evaporation, there's a greater separation of molecules, that volume is greater and remember to talk about difference in energy compared to the latent heat of fusion, you'll do just fine.

Hope this helped!

 

[hassam]

10 times more the signal one..............1250000

i dint understand how u did it...plz explain

 

[hassam]

well http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w02_qp_4.pdf
q1 part b .....is it OVERESTIMATE?
USING LENZ'S LAW, explain why input p.d is out of phase wid output p.d in transformer

 

[SkyPilotage]

As you heat a solid turning it into a liquid, you increase the kinetic energy of its molecules, moving them further apart until the forces of attraction are reduced to allow it to flow freely. Keep in mind the forces of attraction still exists. Now as you heat a liquid, turning it into a gas, the kinetic energy of the molecules are increased to a point where there are no forces of attraction between the molecules.
The energy required to completely separate the molecules, moving from liquid to gas, is much greater that if you were just to reduce their separation, solid to liquid. Hence the reason why the latent heat of vaporization is greater that the latent heat of fusion.
Some confusion arrises from the idea that temperature is a measure of the average kinetic energy of a system, and since the temperature remains constant, the average kinetic energy must also remain constant.
The extra energy required to cause a phase transition is actually potential energy. It is the energy required to overcome the bonds of nearest neighbors to the point that a phase transition can occur. So it really isn't a change in kinetic energy.

But for the exam as long as you know that in evaporation, there's a greater separation of molecules, that volume is greater and remember to talk about difference in energy compared to the latent heat of fusion, you'll do just fine.

Hope this helped!

I thought the kinetic energy does remain constant during a phase change, cz k.e is proportional to temperature change?

 

[SkyPilotage]

i dint understand how u did it...plz explain

Look at how many modulated carrier waves there are between the period of the signal.
One wave of the signal is represented by 10 waves of the carrier.

well http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w02_qp_4.pdf
q1 part b .....is it OVERESTIMATE?

yup , it is, cz you assume all energy goes into the water when it may go to the kettle or the atmosphere.

 

[princesskt]

this is not correct with the supply one should be forward biased and other reversed biased.......with load both should be eiter forward or reversed biased........i m sure .......

 

[hassam]

the question further says when wie is plucked and starts vibrating an alternating voltage trace is observed on cro......question asks why e.m.f is induced
ms says the wire cuts magnetic flux.em.f is induced when there is cutting of flux.......now the problem is with the vagueness of this ms.cos e.m.f is induced when the rate at which flux cuts changes so....he shud have said rate of slux linkage changes as speed of wire changes.....isnt it?

 

[SkyPilotage]

the question further says when wie is plucked and starts vibrating an alternating voltage trace is observed on cro......question asks why e.m.f is induced
ms says the wire cuts magnetic flux.em.f is induced when there is cutting of flux.......now the problem is with the vagueness of this ms.cos e.m.f is induced when the rate at which flux cuts changes so....he shud have said rate of slux linkage changes as speed of wire changes.....isnt it?

No need to argue with ms at this point But when the wire cuts the flux, this means that there is a change in flux. The rate of change of flux will determine the magnitude of the emf.
If the question asked why does the e.m.f change polarity and vary, then you can answer that the rate of change of flux changes with speed!

 

[hassam]

well u mean the meaning of cutting with flux applies to moving wire.....hmm.....ithought if a wire is stationary its still cutting flux.....bt now i understand cutting through means it shud be mooving

 

[SkyPilotage]

How is the anode in an x-ray tube held at earth potential when electrons are accelerated through a voltage?

 

[princesskt]

How is the anode in an x-ray tube held at earth potential when electrons are accelerated through a voltage?

bro...check my statement above graph of the diode was not correct..isn't that?

 

[SkyPilotage]

bro...check my statement above graph of the diode was not correct..isn't that?

please repost the subject of the statement. thank you!

 

[princesskt]

http://www.xtremepapers.com/papers/...nd AS Level/Physics (9702)/9702_w10_qp_42.pdf
q 2 b(iii)

why work done on gas is +240 although the volume is decreasing from p to q.......................

 

[SkyPilotage]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w10_qp_42.pdf
q 2 b(iii)

why work done on gas is +240 although the volume is decreasing from p to q.......................

Exactly! you need to push and exert a force to compress a gas! Therefore you have to make some work to compress it i.e work is +ve!

 

[Vinnyvinvin]

Can anyone help me with p4 mj07 Q10, i have gotten an answer but have no idea how the diagram is suppose to look like. Thanks

 

[kagome]

Can someone please explain me O/N 2010 43 Q 8(b) ??
I saw the MS but still dont understand.. Help needed....

 

[SkyPilotage]

Can anyone help me with p4 mj07 Q10, i have gotten an answer but have no idea how the diagram is suppose to look like. Thanks

no its like this. i did in yellow. View attachment 9109

 

[kagome]

Can anyone help me with p4 mj07 Q10, i have gotten an answer but have no idea how the diagram is suppose to look like. Thanks

I believe its sth like this. Convert the binary number to denary number first.

 

[SkyPilotage]

Can someone please explain me O/N 2010 43 Q 8(b) ??
I saw the MS but still dont understand.. Help needed....

One lamp was used to create photoelectric emission.
Another lamp was just used to increase the light to make it easier to see and observe the experiment.
You need to show that the second lamp used for observation had a frequency less than that of the threshold frequency calculated by the work function E = h x fo !
So there will be no change in the photoelectric current due to the second lamp due to the particulate nature of electrons/particles.