Inverse Square - Overhead Projector
Inverse Square with Light Sensor

 

Code Number: 6B10.20

Demo Title: Inverse Square Law - Diffuse Light Source

Condition: Good

Principle: Inverse Square Law

Area of Study: Optics

Equipment:

Overhead Mask with 4" Hole, Tracing Paper Screen, and Light Meter.

Procedure:

Put the mask with the square hole onto the overhead projector.  At a distance of 1 meter from the screen, the light output of the projector should fill the center 12 in X 12 in square.  Move the overhead back to a distance of 2 meters from the screen and now the light output should fill 4 of the squares.  Move the overhead projector back to a distance of 3 meters from the screen and now the light output should fill 9 of the squares.

Put the mask with the 4" hole on the overhead projector and cover the hole with the tracing paper screen.  Measure the diffuse light coming from the screen with the light meter at measured distances.

References:

  • Isabel Salinas, Marcos H. Giménez, Juan A. Monsoriu, and Juan C. Castro-Palacio, "Characterization of Linear Light Sources with the Smartphone’s Ambient Light Sensor", TPT, Vol. 56, #8, Nov. 2018, p. 562.
  • John Roeder and Art Fovargue, "Vernier Versus TI Sensors", TPT, Vol. 50, #7, Oct. 2012, p. 389.
  • John Roeder, "The Effect of Reflectors on Light Intensity", TPT, Vol. 50, #4, Apr. 2012, p. 246.
  • Haym Kruglak, "Laboratory exercise on the inverse square law*", AJP, Vol. 43, #5, May 1975, p. 449.
  • Robert Ehrlich, "L.13. Departures from the Inverse-Square Law", Turning the World Inside Out and 174 Other Simple Physics Demonstrations, p. 154 - 155.