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Thread: Challenging Optics Problems

  1. #1 Challenging Optics Problems 
    Junior Member
    Join Date
    Sep 2014
    Posts
    1
    Hi

    I have been trying to work these out over the last few days and can get part way through but not get to the final answer. So some help would be appreciated

    1. An unpolarised light beam of 2mm diameter carrying 4mW of power passes through two polarisers. The intensity after the second polarizer is 75W/m^2. What is the angle between the axes of the two polarisers?
    I'm thinking: initial intensity = power/area = 4mW/(4 x pi x (2mm)^2), and then you use final intensity = initial intensity x (cosx)^2, however this gives me the wrong answer from the textbook answer of 70degrees.

    2. A diverging lens of focal length 6mm produces an image of magnification of 1/2. What is the distance between the object and lens?
    I have no idea how to approach this besides knowing 1/f = 1/di + 1/do and magnification = -di/do (correct answer = 6mm)

    3. How many dark fringes can be observed in the diffraction pattern produced by a single slit of width 2.3micrometres with green light of wavelength 535m?
    They don't give us the angle so I don't know how to use the formula dsinx= m x wavelength here. (correct answer = 8)

    Thanks again
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  2. #2  
    Senior Member
    Join Date
    Oct 2013
    Location
    UK
    Posts
    997
    Slaw, think first of all how one polariser affects the intensity of the light.
    Welcome to the forum!
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  3. #3  
    Senior Member
    Join Date
    Jun 2014
    Posts
    551
    Dear Slaw,

    Welcome to the forum!

    This question belongs in the Homework sub forum of this forum. If you place it there you might get answers more readily.
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