This lecture note will make your life ten-fold easier in the scope of the problems it addresses. Consider it a talisman. I discovered this a couple of weeks ago when I was solving these problems for my own conceptual understanding. So I waited till I can completely enunciate the big picture. When I confirmed that its valid for all the following problems I made this note and sharing with you.
What happens when some UV falls on biological molecules? (or any kind) some of these molecules like the wooden pole absorb the energy and there still remains energy which they can emit as visible light. So the UV light kicks the molecules and the molecules in turn emit visible light. This implies that the UV wavelength that the molecules absorbed energy at are very small compared to the wavelength at which they emit visible light. This is always the case.
When we say some materials are fluorescent it means they absorbed higher energy and emitted lower energy radiations of colorful light.
But this has a great deal of application apart from its theoretical interest.
How does the word saturnine derives ! if you care why words derive ! Saturnine might have had originated in the fact that Saturn’s Equinoxes are month long darkness (lack of sunshine for weeks altogether) as Saturn tilts away from sun (and toward sun) for 90 degree (Earth’s 23.44 degree only) ! Thats means parts of sun will get no sun-light for several weeks in the culmination of these Saturnine equinoxes. So saturnine means a person who is gloomy or melancholic. ( — perhaps at-least for longer duration.) I learned this because I was playing with words when grammar of my computer showed the word and I checked its meaning, I was although writing about equinox of Saturn, I came to learn this, cool is it?
Take a chicken tikka stick. (you have seen them right? a few pieces of raw chicken is pierced into a stick)
Now ask yourself the question. How to get it minimally and maximally heated up by the fire from sun. If its minimally heated its winter and if its maximally heated its summer.
Now there are 3 primary parameters that influence the situation. One is called distance from the oven that sun is. Two any change that can be made to this distance is governed by two parameter. one when along a particular direction when we look at the oven how far it is? That distance can be changed a lot due to relative motion of earth and sun. Lets say therefore we will hold the chicken stick quite straight so it goes as straight as we stand on a given location on earth. Thats called a perpendicular in some poor mathematicians dictionary.
2. The object can be a large object, eg say something whose picture you are taking. But as explained above its not the energy of the object (or momentum) which is directly coming into the problem. That would be an added degree of concern if the object is moving with certain velocity, a reason why pictures are blurred. Because motion of objects introduces additional energy-time-momentum-position variables and their corresponding uncertainties. For the argument of the above problem one can imagine the large sized object, lets say a bird, is standing still on a tree while its picture is being taken. In that case if the wavelength of the light [few 100 nano meters = 1/10th of a micrometer] is used (eg in a digital-camera) the corresponding accuracy of the light will be less than micrometers. You can take a very sharp picture of the bird, which is lets say 6 inch long. But when you zoom in to a large degree, the inaccuracies will show up. [in this case how to see a micrometer level image? Is a computer sufficient to show us the uncertain edges of the pixels?] If the wavelength (here visible light) is so small, evidently by de-Broglie relationship, momentum or energy of such light is very large. But its not as large to disturb the feelings of the bird. The bird doesn’t have a problem with visible light, and such energy does not disturb its position or energy or any thing so to say. So while Quantum Mechanics is valid, we are accustomed to say this is a classical mechanics situation. To say QM is invalid is incorrect. To say QM is understood to be valid is a knowledgeable position.