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Light: Refraction, Diffraction, Slits, and Energy Law.

  1. Sep 23, 2015 #1
    Q1. I do not understand why the light has to bend inorder to undergo refraction. My teachers have explained me that, light bends due to the change in velocity. If I change the velocity of a car by half it's original value, I don't find the cars path changing. It does not seem to make sense to me. Why does the light bend?

    Q2. Can light be effected by changing magnetic field.

    Q3. What do you mean by amplitude of light? In the wave nature of light. Does it have to do with the magnitutes of the max. Electric field and max. Magnetic field?

    Q4. Applying energy conservation in the wave nature of light. Suppose I take two really small areas. If I have a light beam with it's electric field and magnetic field at their maximum let that energy be k. After a time t/4 seconds (t being equal to 1/f, where f is the frequency of light) If I try to find the energy using the classical energy density formulas as earlier, I will get 0. I know I am missing something. What is it ?

    Q5. If I have an apparatus, and a magical instruments which are very accurate. If I have thick slits (Thick enough to be 1000 times the thickness of light. If the slits are made of conductors (Assuming their atomic sizes are very very very small). If I pass a light through these slits, with distance between the slits being less then the amplitude of the electric field component of light. What will happen?

    I am sorry for the grammatical errors. Thank you for all the help and support.
  2. jcsd
  3. Sep 23, 2015 #2


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    Q1. Car is not wave. When a beam of light is in oblique incidence on to an interface between different medium, the wavelength changes upon traversing it. The propagation direction must bend in order so that on a wavefront which partially lies in the first and second medium, the wavefront part in the first medium must still be in phase with the wavefront part in the second medium.

    Q2. No

    Q3. In most cases, the amplitude of electric field.

    Q4. The energy for a stationary wave is infinite. You may have forgotten to integrate.

    You cannot compare distance with E field amplitude, they correspond to different physical quantities.
  4. Sep 23, 2015 #3
    Q1. It makes sense when you look at it in that manner. In the text I am currently referring it says 'that the phase difference between two light waves can change if the waves travel through different materials having different indexes of refraction.' What does this statement imply. There was this question regarding the double slit experiment which is quite famous, keeping a material of a good refractive index (A plastic slab, of 1.5 is given as an example question) on one of the slits. It moves the fringe positions.

    Q2. Thank you. :)

    Q3. Thank you. :)

    Q4. I was referring to the energy density at any point. I am sorry for the confusion. Taking the strips of the magnetic and electric energy at their maximum and at their minimum. They do not seem to be equal. This raised a question in my mind, the answer which you just gave, can we equate planks equation to that of the sum of energy densities (Magnetic and Electric) * Volume (Volume of the segment I have chosen)/

    Q5. Thank you, a very silly question indeed.
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