Read Solar Concentrators: Image Size Limits Intensity
A concave mirror collects light through its aperture, but the Sun is not a point source. Its angular size fixes the smallest solar image and therefore limits concentration.
Solar Concentrators and Finite Sun Images is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Start with the condition
Collected power is incident intensity times π r².
Build the governing relation
Set collected power divided by image area equal to the required intensity. The source intensity cancels, leaving a relation between mirror curvature radius and aperture radius.
Finish with a physical check
Check the limiting case before selecting an option: remove the special feature in the diagram or make the relevant parameter very large or very small. The result should reduce to a familiar relation.
OlympIQ exam lens
- ✓State the physical condition before choosing a formula.
- ✓Keep direction, sign and constraint information explicit.
- ✓Test one limiting case before committing to an option.
Focusing all sunlight to a mathematical point ignores the finite angular diameter of the solar disc.
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