Hello sir

Sir please dont reply that this question is out of my expertise please because you studied plhysics and i read that you have thought physics at collage, udergraduate and graduate for many yrs. Sir i know in your expertise column , that you can answer questions related to relativity. But to understand that concept you had learnt physics. So my question is related to physics please answer.

Sir my question is In google i searched sir that laws of reflection are used to construct teslescope ect but sir what is the use of normal and angle of incidence and angle of reflection  in constructing telescope.Sir while scientist first studied about light and reflection how they know to create an angle and normal how they know their uses

please sir please reply. pLease dont reply that it is out of my expertise pleasew help please my humble request to you.

Ashwaraymet, I will be happy to show you how a telescope works. I think you know some physics already. I will describe the major steps in the operation of a telescope for you, and if any step needs more explanation, then you can tell me which steps need more detail, write me again
and I will explain further.

1. There are two major kinds of telescope, one using a mirror where the incoming light hits first, and the other using a lens in front.

2. So you need to know how a single lens makes a small image, or how a curved mirror makes a small image.

3. Then you need to know how a second lens, called the eyepiece, magnifies that image into a large image.

4. So how does an eyepiece lens magnify a small image into  large image. How does a jeweler inspects a watch with a single lens. He just brings the watch up close to his eye. That magnifies the watch. But he cannot focus his eye when the watch is really close. It looks fuzzy. So a lens is used to make a large image farther away from his eye so that he can focus on it. The lens does not really magnify the watch; bringing the watch closer is what magnifies the watch. The lens just helps the jeweler focus on the watch after he brings it close to his eye.

5. Now you can understand how telescopes work. The objective lens, or the curved mirror, both just make a small image of the sky or whatever you want to see close to you, maybe inside the telescope. Then you want to magnify that little image by bringing it close to your eye, like the jeweler does. The eyepiece lens to help you focus.

From your question, I think you want to first understand how light is reflected on a simple plane or curved mirror or refracted by a single lens. Telescopes come later. So choose your topic, reflection or refraction. This explanation is already long, so let's break it down.

Uncle Ben  


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Uncle Ben


I can answer questions regarding Einstein's Theory of Relativity, particularly in Special Relativity. I will not answer homework questions or mathematical problems that require special symbols.


I have taught physics at the college level, undergraduate and graduate, for many years including Special Relativity. I have taught at Johns Hopkins, Case-Western, and MIT. I have also served as a staff member of the Commission on College Physics, which was supported by the National Science Foundation to recommend improvements in the curriculum of college physics departments in the US. I am also the author of a textbook titled Vector Calculus, which was used at MIT in the teaching of electromagnetic theory and relativity. My research interests were mainly in solid state physics, especially the properties of metals at low temperatures. I am listed in the publication known as American Men of Science.

I have dozens of papers published in the Physical Review and in the American Journal of Physics.

I hold a Ph.D. degree in physics from the Johns Hopkins University.

Past/Present Clients
Johns Hopkins University, Case-Western Reserve University, Massachusetts Institute of Technology, Empire State College, Georgetown University, Commission on College Physics, and UNESCO.

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