The discussion centers on the relationship between lens power, focal length, and light focusing. Experiments demonstrated that using denser liquids, such as glycerol, reduced the focal length and increased lens power, resulting in faster paper burns. The inverse square law does not apply in this context, as it pertains to diverging light sources, while the size of the focal spot varies with focal length due to wavefront interference. Shorter focal lengths create smaller images with higher intensity, effectively concentrating light energy more efficiently than longer focal lengths.
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This is an interesting investigation---is it something you thought up, or is it in a science program you are studying at school?Meron35 said:So I've been doing some experiments, using bottles filled with various liquids and timing how long they take to burn paper which is placed at the focal point (where the light was focused).