Hey there! Sign in to join this conversationNew here? Join for free

Edexcel Physics Unit 2 "Physics at work" June 2013 Watch

  • View Poll Results: The last question - Does resistance increase or decrease?
    It increases ( using V=IR or some other method)
    70.73%
    It decreases using the 'lattice vibrations' theory
    29.27%

    Offline

    8
    ReputationRep:
    guys is wavelength directly proportional to speed? which light undergoes greater refraction red or blue?
    Offline

    7
    ReputationRep:
    (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!

    Here's a link to it: http://www.edexcel.com/migrationdocu...e_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
    Offline

    0
    ReputationRep:
    (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 :/
    Offline

    7
    ReputationRep:
    (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
    Offline

    7
    ReputationRep:
    (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
    Offline

    3
    ReputationRep:
    (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
    Offline

    0
    ReputationRep:
    Someone please explain me doppler effect
    Offline

    0
    ReputationRep:
    (Original post by Tomupcraft)
    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

    This is so confusing ! its all about assumptions Thanks alot btw Good luck if u have exam tomorrow (Y) and to everyone
    Offline

    0
    ReputationRep:
    (Original post by Tomupcraft)
    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
    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?
    Offline

    7
    ReputationRep:
    (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!

    Here's a link to it: http://www.edexcel.com/migrationdocu...e_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.
    Offline

    4
    ReputationRep:
    (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.
    Offline

    2
    ReputationRep:
    (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.
    Offline

    8
    ReputationRep:
    (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
    Offline

    8
    ReputationRep:
    (Original post by ArcRaman)
    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.
    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?
    Offline

    8
    ReputationRep:
    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?
    Offline

    2
    ReputationRep:
    A radio station broadcasts at a frequency of 198 kHz.
    (a) Calculate the wavelength of these radio waves
    I know we use v= f x lamda but what is v?
    Offline

    7
    ReputationRep:
    (Original post by alygirl)
    A radio station broadcasts at a frequency of 198 kHz.
    (a) Calculate the wavelength of these radio waves
    I know we use v= f x lamda but what is v?
    velocity of the wave or in this case the speed of light.
    Offline

    0
    ReputationRep:
    (Original post by alygirl)
    A radio station broadcasts at a frequency of 198 kHz.
    (a) Calculate the wavelength of these radio waves
    I know we use v= f x lamda but what is v?
    v is 3 x10^8 as it is radio waves which is an em wave
    so you know frequency and speed so wavelength is easy to calculate

    Posted from TSR Mobile
    Offline

    0
    ReputationRep:
    Doppler effect ??? Someone please explain
    Offline

    2
    ReputationRep:
    (Original post by mickeycharb)
    v is 3 x10^8 as it is radio waves which is an em wave
    so you know frequency and speed so wavelength is easy to calculate

    Posted from TSR Mobile
    Yeah it turns out I was looking at the wrong markscheme whoopsy, as that's what I had originally done haha
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    What's your favourite Christmas sweets?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.