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Light, Wavelength, Space, and the color of Stars

  1. Jun 13, 2012 #1

    Qube

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    Question 1:

    http://i.minus.com/iOmQvqhasiXmx.png [Broken]

    My reasoning is curves 3 and 4. These curves have the biggest relative brightness of orange.

    Question 2:

    Stars are called blackbody radiators because they

    a) never appear perfectly black
    b) always appear perfectly white
    c) reflect most of the light that falls on them
    d) absorb most of the light that falls on them

    Blackbody radiators completely absorb and reemit all incident energy. From this definition, c and d MUST be incorrect. A is also incorrect. By process of elimination, I arrive at b.

    Question 3:

    One student heated a metal wire to produce high speed electrons. When the electrons struck a metal target, waves were produced as shown in the diagram below. What does the student's experiment most likely demonstrate?

    http://i.minus.com/iplmhuT7lwedU.png [Broken]

    a) changing electric fields can produce electromagnetic waves

    b) the direction of transverse waves is always towards the pull of gravity

    c) the direction of electromagnetic waves is always towards the pull of gravity

    d) high speed electrons produce longitudinal waves upon striking a metal target

    I eliminated both B and C because neither transverse nor electromagnetic waves are affected by gravity. That leaves me with A and D. I know A is correct in itself, but I am not sure if it is a correct response to the question and the diagram. I suspect that the answer is A because when high speed electrons strike a metal target they bounce off and produce X-rays, which are EM waves, and EM waves are by definition transverse waves.
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Jun 14, 2012 #2
    So whats the question?

    Err, so why does d have to be incorrect? Do you think the sun appears perfectly white?


    Indeed that would seem to make sense since the wave seems to be moving in air, not in the metal slab. If it were in the metal, it could be a sound wave or whatever.
     
    Last edited by a moderator: May 6, 2017
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