Suppose that you look into a photometer's eyepiece and the fluorescent disks appear to be equal in intensity. If the distance between the photometer to lamp 1 is 400mm, the distance between the photometer to lamp 2 is 200 mm, and the intensity of lamp 2 is known to be 15 candelas, what is the intensity to lamp 1?

Question

Mckinley Clark

Physics

21 February, 05:47

Suppose that you look into a photometer's eyepiece and the fluorescent disks appear to be equal in intensity. If the distance between the photometer to lamp 1 is 400mm, the distance between the photometer to lamp 2 is 200 mm, and the intensity of lamp 2 is known to be 15 candelas, what is the intensity to lamp 1?

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Denise Henderson · Answer 1

Use the Inverse square law, Intensity (I) of a light is inversely proportional to the square of the distance (d).

I=1 / (d*d)

Let Intensity for lamp 1 is L1 distance be D1 so on, L2 D2 for Intensity for lamp 2 and its distance.

L1/L2 = (D2*D2) / (D1*D1)

L1/15 = (200*200) / (400*400)

L1=15*0.25

L1=3.75 candela