Edexcel Physics Unit 2 "Physics at work" June 2013

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Reply 480

jollygood

guys is wavelength directly proportional to speed? which light undergoes greater refraction red or blue?

Reply 481

Tomupcraft

Original post by Arnold.L

Could anyone explain question 16 from January 2009 paper please? Both parts if possible and in as much detail as you can! :biggrin:

Here's a link to it: http://www.edexcel.com/migrationdocuments/QP%20GCE%20Curriculum%202000/January%202009/6PH02_01_que_20090115.pdf

Thanks in advance.

Part A
It is a series circuit therefore current is the same at every point hence current is equal in both lamps
If lamp B glows more brightly the Power must be greater. P=VI, I is constant so V must be greater so pd across lamp A is less the pd across lamp B as B glows more brightly
V=IR, As I is constant for both lamps and we know that V is greater for lamp B then R must also be greater for lamp B therefore the resistance of lamp A is less than the resistance of lamp B

Reply 482

arshia

Original post by Tomupcraft

mu = refractive index

mu = sin i / sin r

sin i = 35 degrees as it must be angle to normal
sin r = 90 degrees as it is refracted along the boundary

mu = sin35 / 1
mu = 0.57 but this mu is for the glass to the air, it wants it for the air to the glass therefor mu for glass = 1/0.57 = 1.74

but its not mentioned that find for the air to the glass :/

Reply 483

Tomupcraft

Original post by jollygood

guys is wavelength directly proportional to speed? which light undergoes greater refraction red or blue?

v=f*lambda

No as v is constant for light. However wavelength is inversely proportional to frequency

Blue undergoes the greatest refraction.

Sorry Edit: My example is only true for EM radiation

(edited 10 years ago)

Reply 484

Tomupcraft

Original post by arshia

but its not mentioned that find for the air to the glass :/

I had this problem when I did the question. So im just assuming that when they say find the refractive index for a material, they are wanting that material to be the material that refracts the light if you understand.

Eg. take air and glass
if they say find mu of glass I would assume light is travelling from air to glass
but if they say find mu of air then assume light is travelling from glass to air

Reply 485

Freddy-Francis

Original post by jollygood

guys is wavelength directly proportional to speed? which light undergoes greater refraction red or blue?

speed = wavelength * Frequency

so as speed increases, the frequency also increases. As frequency increases, then the wavelength decreases

Reply 486

Gunner121

Someone please explain me doppler effect

Reply 487

arshia

Original post by Tomupcraft

This is so confusing ! its all about assumptions :frown:

Thanks alot btw :smile:

Good luck if u have exam tomorrow (Y) and to everyone :smile:

Reply 488

Arnold.L

Original post by Tomupcraft

Cheers for the quality answer! Exactly the sort of answer I needed haha, the mark schemes don't help much :P

Have you got any ideas about part B?

Reply 489

Tomupcraft

Original post by Arnold.L

Could anyone explain question 16 from January 2009 paper please? Both parts if possible and in as much detail as you can! :biggrin:

Here's a link to it: http://www.edexcel.com/migrationdocuments/QP%20GCE%20Curriculum%202000/January%202009/6PH02_01_que_20090115.pdf

Thanks in advance.

For part B
When in parallel voltage across both of the bulbs is the same.
However current splits
We know that lamp A has a lower resistance than lamp B and therefore using V/R=I can see that I is greater for lamp A, so P=VI, V is constant but I is greater for lamp A so power is greater for A and hence will be brighter in parallel.

Reply 490

CharlieTT

Original post by jollygood

guys is wavelength directly proportional to speed? which light undergoes greater refraction red or blue?

When light travels through an interface its speed changes but frequency remains the same. So if the new medium is denser, the speed decreases so the wavelength also decreases.

Blue light slows down more than red light so it is refracted more than red light in a denser medium.

Reply 491

ArcRaman

Original post by jollygood

guys is wavelength directly proportional to speed? which light undergoes greater refraction red or blue?

BBB - blue bends better
RBR - red bends rotten.

Therefore you can see that if blue and red light travel in the same media, other than vacuum, blue light will always have to experience a greater index of refraction.

Reply 492

jollygood

Original post by Tomupcraft

v=f*lambda

No as v is constant for light. However wavelength is inversely proportional to frequency

Blue undergoes the greatest refraction.

Sorry Edit: My example is only true for EM radiation

thanks very much :smile:

Reply 493

jollygood

Original post by ArcRaman

that's the best way to remember. thanks. when we say grestest refraction it means bends away from the normal. angle between the normal and refracted ray is big. correct me if I am wrong?

Reply 494

jollygood

is there any genius person who would like to tell me how do we make up the frequency and wavelenghth formulas in case of open ended tubes and close ended tubes or closed at one end ? my teacher didn't go through this topic at all. ?and also the no. of nodes and antinodes in each case?