Skip to main content


Showing posts from March, 2014

How weightlessness experiment in a satellite overcome? Give relevant formula

In order to produce an artificial gravity in the space craft, the laboratory of space craft is rotated with suitable frequency about its own axis. The rotation is so maintained that the astronaut do not feel weightlessness. The frequency of rotation depends on the length of laboratory of space craft.


Consider a space craft whose laboratory is 'L' meter long consisting of two chambers connected by a tunnel. Let us see how many revloutions per second must the space craft make in order to supply artificial gravity for the astronauts.
Let 'T' be the time for one revolution and 'f' be the frequency of rotation.

R = L / 2 --------(i)
When the laboratory revolves, a centripetal force is experienced by the astronauts.

  Fc = mv2/r --------(ii)
According to Newton's second law of motion

Fc = mac --------(iii)
Comparing equations (ii) and (iii)

mac = mv2/r
ac = v2/r
Where ac is the centripetal acceleration
Since radius of laboratory is R , therefo…

If the tension in string is doubled what will be the effect on the speed of standing waves in the string?

The velocity of a travelling wave in a stretched string is determined by the tension and the mass per unit length of the string.

The wave velocity is given by

When the wave relationship is applied to a stretched string, it is seen that resonant standing wave modes are produced.

So, if we double the tension the speed will increase 1.41 times or root (2) times.

At what condition a convex lens can behave as a diverging lens?

The ability of a lens to act as converging or diverging depends upon its refractive index. The refractive index n of the material of a lens depends upon the medium in which the lens is placed. Generally the lens is in air so n gives refractive index of material of lens with respect to air. If you place the convex lens in a medium other than air, then due to change in n, the focal length f of lens changes. if n decreases, f increases.

So if you immerse the convex lens in a liquid whose refractive index is greater than refractive index of material of lens then it will change its nature and become concave lens and thus it will start diverging the rays rather than focusing them on a single point. Its true the other way round also that is concave also becomes convex.

We show degree on centigrade and not show on kelvin why??..what is reason behind it??

The Kelvin temperature scale is sometimes called the absolute temperature scale, especially in older books. It was developed byWilliam Thomson, also known as Lord Kelvin, in 1848. A Kelvin degree is the same size as a Centigrade degree. This temperature scale however uses absolute zero, rather than the freezing point of water, as the zero point. In this temperature scale water freezes at 273.15 Kelvins and boils at 373.15 Kelvins. The Kelvin temperature scale should be used in thermodynamic calculations. Its principle difference is that kelvin measurements, written as K have a much lower starting point: 0K or 0 Kelvin (note the absence of the degree symbol °).

It bears additional mention that kelvins are not measured by degrees. They were considered so until 1968, when the 13th General Conference on Weights and Measures determined to drop the degree reference. This decision was made because Thomson’s measurement referred to an absolute and specific temperature (where no heat energy e…

Give difference between inertial and non inertial frames of references?

Inertial Frame of Reference:
Inertial frames are ones which are at rest or moving with uniform velocity with respect to fixed stars.
For an observer in such a frame of reference Newton's second law of motion is valid.

Ex: A train moving with uniform velocity is an inertial frame.

Non Inertial Frame of Reference: A non inertial frame is one which is accelerated ( linearly or due to rotation) with respect to fixed stars.
Newton's second law of motion is not valid in such a frame of reference, unless we introduce a force called pseudo - force.

Ex: A freely falling elevator may be taken as a non inertial frame.
For Example:

Wave Particle Duality and Uncertainty Principle

The wave-like nature of light explains most of its properties:

1. Reflection/refraction


3.Doppler effect

But, the results from stellar spectroscopy (emission and absorption spectra) can only be explained if light has a particle nature as shown by Bohr's atom and the photon description of light.
This dualism to the nature of light is best demonstrated by the photoelectric effect, where a weak UV light produces a current flow (releases electrons) but a strong red light does not release electrons no matter how intense the red light.

Einstein explained the photoelectric effect by assuming that light exists in a particle-like state, packets of energy (quanta) called photons. There is no current flow for red light because the packets of energy carried by each individual red photons are too weak to knock the electrons off the atoms no matter how many red photons you beamed onto the cathode. But the individual UV photons were each strong enough to release the e…