Investigation of Light Intensity

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  • Topic: Angle, Ray, Angle of incidence
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  • Published : November 24, 2012
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Investigations in Light Intensity Change through Angular Displacement Guiding Question
How does the intensity of light change as the angle of incidence to the light source increases?
Prediction of Results
Predict what you think will happen and what type of equation and graph might best fit the data representing the intensity of a light as the angle of incidence increases. Objective
After completing this lesson, a student should be able to analyze light intensity striking a surface at varying angles of incidence.
CBL, TI-83 Plus calculator, light sensor, lamp with light bulb (60 to 100 watts), tape measure, Scotch tape (or similar), protractor, sheet of paper, ANGLE program, daily log Vocabulary
the normal

angle of incidence periodic

sinusoidal regression

You have completed an investigation of light intensity changes with varying distance. You will continue investigating intensity changes, but now you will note the change of intensity as light strikes a surface through increasing angles of incidence. As Figure 1 indicates, the angle of incidence is the angle at which light strikes a surface. The normal is an imaginary line perpendicular to the plane on which light strikes. The angle of incidence is the angle between the normal and an incident (that is, an incoming) light ray.

Angle of incidence

Incident Light

Figure 1
As the angle of incident light increases, is it more reasonable to think that its intensity increases or decreases? As you think about this question, consider whether you are more likely to get a sunburn in the late evening when the sun is low on the horizon

(greater incidence angle) or at noon time when the sun is more overhead (smaller incidence angle), as sketched below? Is it usually hotter at noon or in the late evening?

Evening Sunlight

Noon Sunlight

If you suspect that intensity decreases with increasing angle of incidence, you are on the right track. Assuming for the...
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