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1. The inverse law states that the intensity of illumination is inversely proportional to the square of the distance from the point source.

I  _1_
d2

A student carried out an investigation, measuring a set of intensity readings ( I ) on a light meter at various distances ( d) from a point source of light. The results are shown in the table below :

Intensity ( I ) W/m2 15 48 116 249 442 761
distance ( d ) cm 114 64 41 28 21 16
1/distance2 ( 1/d2 ) cm-2
1/distance2 ( 1/d2 ) cm-2 X10-5

9a) Plot a graph of intensity ( y-axis ) against distance ( x-axis ).What
does this graph indicate ?

9.b) Plot another graph of intensity (y-axis) against 1/ d2 (x-axis)

9c) Using the results , develop a relationship between ( I ) and ( d )
and hence prove that the inverse law holds. Remember I x d2 = Constant

9 d) Find the gradient of the graph in (b).

9e) Find the gradient of the graph in a) when d = 45 cm by drawing a tangent to the line and drawing a tangent to the line.
2. (Original post by mark000)
The inverse law states that the intensity of illumination is inversely proportional to the square of the distance from the point source.

I  _1_
d2

A student carried out an investigation, measuring a set of intensity readings ( I ) on a light meter at various distances ( d) from a point source of light. The results are shown in the table below :

Intensity ( I ) W/m2 15 48 116 249 442 761
distance ( d ) cm 114 64 41 28 21 16
1/distance2 ( 1/d2 ) cm-2
1/distance2 ( 1/d2 ) cm-2 X10-5

9a) Plot a graph of intensity ( y-axis ) against distance ( x-axis ).What
does this graph indicate ?

9.b) Plot another graph of intensity (y-axis) against 1/ d2 (x-axis)

9c) Using the results , develop a relationship between ( I ) and ( d )
and hence prove that the inverse law holds. Remember I x d2 = Constant

9 d) Find the gradient of the graph in (b).

9e) Find the gradient of the graph in a) when d = 45 cm by drawing a tangent to the line and drawing a tangent to the line.
What have you tried? What is your actual question?

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Updated: January 24, 2017
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