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Formula for a torch

  1. Jun 17, 2010 #1
    Hi i'm new here and I'd like some help with something that's been niggling me for the past few days. I've yet to study Maths or Physics at A Level (UK), so this should be easy for some of you.

    If I were to shine a torch that shone a circular, even spreading of light, what would be the relationship between the angle of the light coming from the torch, the distance from a wall, and the brightness on the wall?

    Here's what i've got: (this is assuming there isn't a property of light that I don't know about)

    D=Distance from wall
    X=Angle, As in Shining at 90 degrees would actually shine 90 up and 90 down


    D*TanX=Radius, so pi*r*r=a


    However it just doesn't seem right. Is this right or wrong?
    Last edited by a moderator: Apr 25, 2017
  2. jcsd
  3. Jun 17, 2010 #2


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