Question

A magnifying glass used to focus sunlight in an intense hot spot becomes a burning glass or solar collector. If the lens is made larger and/or if the focus is made more concentrated, the hot spot gets hotter. Could a lens be made bigger and bigger or could its focus be made more and more concentrated so that its hot spot would be hotter than the sun itself

Answer 1

we use the diffraction criterion, the temperature of the sun cannot be reached.

Step-by-step explanation:

In order to answer this question, we must shorten the resolution limit given by diffraction, that is the smallest point that we can focus on.

θ= 1.22 λ/D

This value of angle is the smallest that can focus a lens of Diameter D, when analyzing this expression we see that if we increase the diameter the value of the angle decreases.

On the other hand, the angle increases with the wavelength used, remember that the infrared range (λ> 700 nm) are the rays that heat the most.

Therefore we see that we have two processes that are opposite, it depends on which one is more important, we have a different but finite diffraction limit, therefore IT IS NOT POSSIBLE TO COLLECT ALL THE ENERGY IN ONE POINT.

On the other hand, the Earth's atmosphere reflects a very high amount of the Sun's energy.

In conclusion, if we use the diffraction criterion, the temperature of the sun cannot be reached.