Author Topic: Edexcel PHYSICS Doubts  (Read 135955 times)

Offline Saladin

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Re: Edexcel PHYSICS Doubts
« Reply #30 on: May 11, 2010, 03:39:50 pm »
here's a question i need help solving:
A student observes the diffraction of white light by holding a diffraction grating close to her eyes
a)draw a simple diagram to illustrate what the student observes
b) a tube of KMn04 solution is placed in front of white light source.Then the student views the filament through the solution with the grating close to her eyes. she notices that the blue, yellow and orange colors have vanished. Give an explanation.

Can you please help me asap? Thanks ! :)

(a) A variety of colours, like that of a rainbow, all mixed up in one place.
(b) The light will be polarised. This means that the vibrations that have caused the other different colours of light no longer vibrate due to this polarisation.

Offline Darth Austrakast

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Re: Edexcel PHYSICS Doubts
« Reply #31 on: May 11, 2010, 04:17:47 pm »
thanks
but i wrote exactly same for the last answer but still got wrong
but thanks a lot for confirming it  :)
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Offline vanibharutham

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Re: Edexcel PHYSICS Doubts
« Reply #32 on: May 11, 2010, 06:13:07 pm »
Maybe certain colours of the white light have been absorbed by the purple colour of potassium permanganate solution. I doubt that KMnO4 will be optically active... and thus will not polarize light... i know for sure that organic molecules like sucrose and glucose are optically active.. they demonstrate chilarity, but KMnO4 is ... ionic solution....
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Offline vanibharutham

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Re: Edexcel PHYSICS Doubts
« Reply #33 on: May 12, 2010, 07:03:50 pm »
i got it!

absorption spectra

the KMnO4 solution must have electrons that get excited whenever there is blue, yellow or orange light.
The excited electrons return to ground state and reemit the light equally in all directions. To an observer with a diffraction grating it seems like there is no orange, yellow or blue because the intensity is soo less
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Offline Saladin

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Re: Edexcel PHYSICS Doubts
« Reply #34 on: May 12, 2010, 07:07:10 pm »
i got it!

absorption spectra

the KMnO4 solution must have electrons that get excited whenever there is blue, yellow or orange light.
The excited electrons return to ground state and reemit the light equally in all directions. To an observer with a diffraction grating it seems like there is no orange, yellow or blue because the intensity is soo less

It has to be optically active then, which it is not. I believe your first point was correct.

Offline wakemeup

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Offline vanibharutham

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Re: Edexcel PHYSICS Doubts
« Reply #36 on: May 16, 2010, 08:59:40 pm »
Photoelectric Effect...

Ill write down a model answer if you must have one:

"The debate about the true nature of light was "resolved" when Loius de Broglie proposed the wave-particle duality theory. The photoelectric effect demonstrates the particle like properties of light.

If we assumed a wave model, the observations seen could not be explained. We know that the energy of a wave is proportional to the intensity. Therefore, increasing the intensity should increase the kinetic energy of the particles released. But this is not seen. What is seen is that MORE photoelectrons of the SAME kinetic energy are released.
Also, waves transfer energy continuously. If a light wave continuously transmitted energy to a metal, eventually the electrons would gain enough energy to escape the metal. Thus the frequency would not matter. However, this is not the case and electrons are not emitted below a certain threshold frequency.

A particle model of light can explain these observations. If we assume light is made up of particles known as photons (quanta of EM radiation) that have a discrete amount of energy denoted by E = hf. We can see that by increasing the frequency we increase the energy of a photon. And thus by increasing the frequency, the SAME number of photoelectrons are released but of a higher kinetic energy. Because one photon interacts with only one electron, the energy is transmitted and a higher KE of the photoelectrons is seen.
Every metal has a work function - the minimum amount of energy required to JUST cause photoemission. If the energy of photons is not greater than the work function, no photoemission occurs. Because E is proportional to f, below a certain frequency the photons dont have enough energy to cause photoemission."


Haha that was good revision :)
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Offline Darth Austrakast

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Re: Edexcel PHYSICS Doubts
« Reply #37 on: May 19, 2010, 04:28:36 pm »
hey thanx man dat was a nyc revision  ;D
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Offline Darkstar3000

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Re: Edexcel PHYSICS Doubts
« Reply #38 on: May 25, 2010, 11:50:13 am »
Useful data :
                                                      Energy stored per unit mass J/kg
Modern spring steel                                           130
Tendon in leg                                                  2500
Rubber chord                                                  8000


show that a car of mass 1200 kg would need steel springs of total mass approximately equal to 3kg to store energy when it encounters pot-holes of depth 3cm

how do i solve this

and

The sum of the mass of leg tendons of a skier might be of the order of 04.kg. Estimate the size 'bump' that a skier of mass 75kg could theoretically negotiate
« Last Edit: May 25, 2010, 11:53:02 am by Darkstar3000 »

Offline T.Q

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Re: Edexcel PHYSICS Doubts
« Reply #39 on: May 25, 2010, 12:26:37 pm »
from where did u got this question
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Offline Darkstar3000

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Re: Edexcel PHYSICS Doubts
« Reply #40 on: May 25, 2010, 12:41:16 pm »
from where did u got this question

It says jan 02 at the top, my teacher collected some papers with stuff that is in the syllabus for us to solve and this is one of the questions

Offline ABF

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Re: Edexcel PHYSICS Doubts
« Reply #41 on: May 25, 2010, 02:13:41 pm »
does anyone have any notes for revision for physics 6PH01...

Offline wakemeup

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Re: Edexcel PHYSICS Doubts
« Reply #42 on: May 25, 2010, 03:56:02 pm »
Could someone please explain 22ci and ii of the edexcel sample paper. According to the mark scheme T=wsin40 which doesn't make any sense. My perception of the diagram is probably wrong.

Offline Igcseboy

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Re: Edexcel PHYSICS Doubts
« Reply #43 on: May 26, 2010, 08:44:16 am »
Hey

2morrow is the 6PH01 paper

so i have some questions

in free body diagrams from where we should draw the contact force??

and anybody have notes on projection.....

any important points on the speed time graphs and all ???

i can understand wat to do as the portion for unit 1 is too small i guess

any suggestions on wat i shud do

Offline Darth Austrakast

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Re: Edexcel PHYSICS Doubts
« Reply #44 on: May 26, 2010, 06:38:07 pm »
Hey

2morrow is the 6PH01 paper

so i have some questions

in free body diagrams from where we should draw the contact force??

and anybody have notes on projection.....

any important points on the speed time graphs and all ???

i can understand wat to do as the portion for unit 1 is too small i guess

any suggestions on wat i shud do


the normal reaction force should always be a normal to the/perpenicular to center of gravity

here r some stuffs on projectiles
http://www.astarmathsandphysics.com/a_level_physics_notes/forces_and_motion/a_level_physics_notes_equations_for_projectiles.html

if u still have problem with free body force diagram
take a look 2 this http://www.astarmathsandphysics.com/a_level_physics_notes/forces_and_motion/a_level_physics_notes_free_body_diagrams.html





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