Search results

  1. A

    Counts in a geiger counter

    One thing is not clear to me. When alpha or beta or gamma radiation enter into geiger counter, it ionizes the gas and ionization current produces counts in the detector. What exactly this counts indicate? Does it show the number of alpha or beta particles enter into the tube? Since even if one...
  2. A

    Why canal rays need a perforated cathode?

    In the cathode ray production experiment, at about .01 mm of Hg, cathode rays travel from cathode and move towards anode and produce fluorescence on the walls near the anode.At the same time canal rays also move towards cathode. But only when you use a perforated cathode, the canal rays...
  3. A

    Ratio of charges in thomson expt

    Homework Statement three particles having charges 1:2:3 produce the same point on the photographic film in the thomson experiment. The masses are in the ratio of a) 1:2:3 b)3:2:1 c) 2:3:1 d) 1:3:2 Homework Equations a = F/m = Eq/m The Attempt at a Solution Since all the...
  4. A

    Seebeck effect

    In thermoelectric series, lead is arranged in the middle and other metals arranged both on the left and right hand side of lead. Lead does not exhibit Thomson effect. If you take a metal on the left of lead and another metal on its right, the thermo electric current flows according to certain...
  5. A

    Meissner effect

    I need clarifications on Meissner effect. 1. According to this theory, when any diamagnetic substance is cooled below its critical temperature, it becomes a superconductor and it expels magnetic flux from inside. Is it applicable only to a diamagnetic substance or ferromagnetic substances...
  6. A

    Gauss theorem and the nature of the surface

    According to Gauss’ law the total number of lines of force over a closed surface is equal to 1/ε times the net charge enclosed within the closed surface. Why should it be a closed surface but not an open surface too? I am unable to find a convincing explanation for it. Since we take into...
  7. A

    Source of energy in fusion reactions

    In the case of nuclear fission, when U-235 splits into Ba,Kr and three neutrons , then it is shown that the total mass of the products on the right side of the equation is slightly less than that of the reactants on the left side. So this missing mass-the mass defect – is converted into energy...
  8. A

    Higgs boson and the future of quantum phyiscs

    Can anybody throw light on the following doubts? 1.what is the implication of the recent discovery of the higgs boson in the quantum physics? Does it support the quantum nature of matter and wave and the uncertainty principle? 2. It is said that Einstein did not accept the quantum theory...
  9. A

    Alpha ray scattering experiment

    I have some basic doubts in the alpha ray scattering experiment by Rutherford and his students way back in 1909. 1.In the formula for the distance of the closest approach, the term velocity of the alpha particle and the charge of the gold nucleus appears. How did they measure the velocity of...
  10. A

    Polaroids in head lights

    I have studied,as one of the uses of polaroids is, that it can be fitted in the head lights of cars and other vehicles to eliminate the glare. This will certainly act as a boon to the motorists and result in considerable reduction of road accidents during the night time. I have also learnt...
  11. A

    Carbon di oxide emission of filament bulbs

    One thing I am not able to understand. Governments advocate the slow phasing out of the filament lamps and replacing them with CFLs.The reason repeatedly cited for this is that the filament lamps contribute to the global warming by way of emitting carbon-di-oxide. But, interestingly, it is...
  12. A

    Cathode ray tube

    In a video demonstration (not animation), cathode rays appear as a beam of green light moving from the cathode to anode inside the tube. The demonstrator brings a magnet near the tube and the green beam deflects. This I can understand. What I can not understand is that how the electron beam...
  13. A

    Pre emphasis net work

    I will be thankful if any one clears the following doubts in the concept of pre-emphasis in a FM transmitter in a simple way. 1. In the higher secondary physics text book published by Tamil Nadu government, regarding the pre-emphasis net work, it is given as follows:"Since the modulating AF...
  14. A

    Output impedance

    The concept of output impedance is highly confusing to me. I will be thankful if some body gives simple explanations to the following. 1. I undertand that in the case of current amplifiers, the out put impedance should be low and the input one should be high. In the case of voltage...
  15. A

    Radio active decay

    I need some clarifications on the following concepts: 1.When an α-particle is released by a radio active sample, it loses a charge of +2. Similarly, when it loses a β particle it gains one positive charge. But there is no change in the number of electrons in the outer orbits of the radio...
  16. A

    Mass spectrometer

    When different masses are accelerated by the same potential,the lighter mass should move with a greater velocity than that of the heavier one. But, how in the velocity selector in the Bainbridge mass spectrometer, different masses(isotopes) come out with same velocity?
  17. A

    He-Ne laser

    I have some serious doubts regarding He-Ne laser: 1. In He, the ground state energy value is taken is 0 eV and the meta stable state is taken as 20.61 eV. similarly in Ne the meta stable levels are taken as 20.66 and 18.7 eV respectively. How these values are arrived at? In Bohr's expression...
  18. A

    NASA Slowing of a satellite sent by Nasa

    There is a story doing round in e-mails and FB recently. The story is this: A satellite sent by Nasa, while going round the globe, slows down automatically when it crosses a particular spot over the Saneeswarar temple (a Hindu temple dedicated for Saturn), in Thirunallar, Tamil nadu, India...
  19. A

    Elastic collision

    In an inelastic collision, it is said that the total KE is not conserved but the total momentum is. When both the momentum and KE are the products of mass and some power of velocity, how total value of one remains constant and the other not. This is very confusing.
  20. A

    Moment of force

    Are the 'moment of a force' and the 'moment of a couple' are technically same or different? Because, the latter is called by a special term 'torque'. Both terms are confusing, as the first is measured by the product of the force and its perpendicular distance from the fulcrum where as the...
  21. A

    Ac circuit with an inductance

    In an a.c.circuit containing only inductance, for example, it is said that the current is lagging behind emf by 90 degree. We can understand this that when the emf is zero,the current is at its negative maximum and when the emf reaches its positive maximum, the current becomes zero and so on...
  22. A

    Electric flux force lines

    The electric flux around a charge is represented by electric lines of force. But it is said that the electric lines of force is purely an imaginary concept to visualize a field. In the Gauss' law, using the formula q/epsilon we calculate the total number of lines of force. For a charge of 1...
  23. A

    Deriving the lens formula for a convex lens-say

    I will be thankful if the following points are clarified. 1. While deriving the lens formula for a convex lens-say, 1/f= 1/v - 1/u where u and v are the object and image distances, the minus sign is obtained after applying sign conventions. But, I don't understand the logic behind taking the...
  24. A

    A heated blue glass

    When a piece of red glass is heated to high temperature, it glows green. Similarly, when a green glass is heated to high temperature, it glows red. But How does a blue or yellow glass glow when heated? I could not find the answers for this when I browsed.
  25. A

    Reversible and irreversible reactions

    I need some clarification on the following points on the reversible and irreversible reactions. In the examples cited in text books, for reversible reaction, isothermal expansion and compression are given. But the adiabatic exp and comp are not given. Why is it not included in the list...
  26. A

    Kinetic theory

    I have some questions on kinetic theory of gases: kinetic theory assumes that the inter molecular force of attraction between two molecules of a gas is negligible. This assumption applies to the condition that the said gas is either at low pressure or at high temperature. This means, when the...
  27. A

    Band theory of solids

    I have a serious doubt about the concept of band theory of solids. While explaining the behaviour of semi conductors, the following explanation is given. "The valency bands are completely filled electron-bands, where as the conduction band is usually empty. The conduction takes place when a...
  28. A

    Nuclear reactor

    Regarding nuclear reactor I need some clarifiications; 1. During fisssioin of U-235 it is said that the temperature raises to several million degree celcius (in uncontrolled chain reation). But what will be temperature produced when a controlled chain reaction takes place inside a nuclear...
  29. A

    Twin paradox and other things

    Friends, I will be happy if any body throws light on the following concepts: (1). In the case of time dilation it is said that a clock in a moving frame appears to go slow to an observer in a resting frame.It leads to the famous twin paradox in which 'A' who spends some time in a space ship...
  30. A

    Stokes' law experiment

    I am not able to understand the following situations. In stokes' experiment a tiny lead shot falls freely under gravity in a highly viscous column of liquid. When the viscous force becomes equal to the net weight of the lead shot it is said that the shot moves down with a constant...