logearav

Thanks for the replies. But i have reproduced the question asked in competitive exam held for recruiting teachers , verbatim. No additional details are given either. To ease out the confusion, i posted in this forum so that learned members can clarify

Two photons are travelling, one in the east and another in the west. Then the relative velocity between two is (a) 2c (b) c/2 © c^2 (d) c I know the velocity of light is constant, i presume the answer is option (d). But the term relative velocity confuses me. I look forward for revered members' help in this regard

What do you mean by Gain medium,sir?

Thanks again. Now the stimulating photon travel along the axis of mirror, it gets reflected from one side of the mirror and gets incident on other atoms and the lasing action starts. In what way, the reflection from the mirror helps in amplifying the laser signal?

Revered Members I have attached images of applications of Gauss' law namely 1) Electric field due to an infinitely long charged wire and 2) Electric field due to an infinite charged plane sheet. In both cases Gaussian surface is cylinder. In the first case, the electric flux is found for curved surface and it has been done for only side that is right side of cylinder in this case. In the second case, the electric flux is found for plane caps but it has been done for both the left plane cap and right plane cap. My doubt is , why we are doing for only one side for the curved surface and for both sides in the case of plane caps?

Thanks for the reply Swansont. Wikipedia says "At the nuclear level, binding energy is also equal to the energy liberated when a nucleus is created from other nucleons or nuclei. ". Why the energy released is more for binding nucleons for smaller nuclei when compared to heavier nuclei"

They are due to balancing of the Centripetal force and Electrostatic force of attraction

Revered Members, Binding energy for lighter nuclei is large and for heavier nuclei BE is less. Why? I know BE is the energy needed to bind protons and neutrons in a nucleus. Also it can be defined as the energy that must be supplied to disrupt the nucleus into constituent protons and neutrons. Take a lighter nuclei which has 3 protons and so ideally the energy needed to bind these 3 protons should be less when compared with the energy needed to bind 82 protons(say) in a heavier nuclei . So, why BE is less for heavier nuclei than lighter nuclei?

When we consider a beaker of water and two molecules, one completely inside the water and the other at the free surface, the water molecule at the free surface will experience net downward force of attraction and this causes the water molecule to behave like a stretched membrane, which is called as surface tension. Now to bring this molecule at the free surface to interior of beaker, one has to do work against the force of attraction and this is stored as potential energy. Water molecule acquires minimum surface area to have minimum potential energy. What is the relation between surface area and potential energy? More work done so more potential energy and more surface area. But how surface tension correspond to minimum potential energy. I can't understand.

Thanks a lot swansont. Now i understood by your analogy with water in a cup. Thanks a ton. Now i could grasp. People like you is an asset for this forum.

The Fermi Level is defined as the highest occupied molecular orbital in the valence band at 0 K, so that there are many states available to accept electrons, if the case were a metal. Thanks swansont. Fermi Level is the highest occupied molecular orbital. I can't understand " so that there are many states available to accept electrons". Let me have a try. If fermi level is occupied , then how it is possible to say many states are available to accept electrons, because fermi level is the highest level and also occupied so no state can exist above fermi level. Sorry for stretching you, i am a novice. Thats why i ask for explanation.

Sir, I can't understand. Could you elaborate, please?

Why none has answered my query?

Revered Members, Can i know what is meant by fermi level? I googled this, but i could not understand. One site says Fermi level as top of collection of electron energy levels at absolute zero. As far as my knowledge I know electron energy levels as K, L,M, N etc with energy values -13.6eV, -3.4eV etc. Top of collection means, is it O eV?

thanks swansont. My doubt is an electron which comes to metastable state has already has one photon absorbed in it which was supplied when the electron was in ground state. My question is, do we supply one more photon to this electron which has one absorbed photon already? I mean where the stimulating photon comes from? Do we supply externally?