A budding magician holds a 2.24-mW laser pointer, wondering whether he could use it to keep an object floating in the air with the radiation

Question

A budding magician holds a 2.24-mW laser pointer, wondering whether he could use it to keep an object floating in the air with the radiation pressure. This might be an idea for a new trick! Assuming the laser pointer has a circular beam 3.00 mm in diameter and the magician rigs up a totally reflecting sail on which to shine the laser, what is the maximum weight the magician could suspend with this technique?

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Jezebel 5 years 2021-07-24T11:45:36+00:00 1 Answers 19 views 0

Answers ( )

  1. Euphemia
    0
    2021-07-24T11:46:51+00:00
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    Answer:

     W = 1.49 10⁻¹¹ kg

    Explanation:

    For this problem, let’s use Newton’s equation of equilibrium

               F – W = 0

                F = W              (1)

    Strength can be found from the definition of pressure

            P = F / A

            F = P A

       

    The radiation pressure for a reflective surface is

                P = 2 I / c)

       

    We substitute in equation 1

             2 I / c  A = W

    The intensity is defined by the ratio of the power between the area

              I = P / A

              P = I A

    We substitute

              2 P / c = W

       

               W = 2  2.24 10-3 / 3 108

               W = 1.49 10⁻¹¹ kg

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