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## Path dependence of Thermodynamic Variables

In NCERT TEXT BOOK it is written that
Since U is a state variable, ΔU depends only on the initial and final states and not on the path taken by the gas to go from one to the other. However, ΔQ and ΔW will, in general, depend on the path taken to go from the initial to final states. From the First Law of Thermodynamics,it is clear that the combination ΔQ – ΔW, is however, path independent.

ΔQ and ΔW will, in general, depend on the path taken ??andΔQ – ΔW, is however, path independent.
explain?? how?? ## The Physics of Accidents

Accidents

Why are road accident at high speeds very much worse than accidents at low speeds?

As you might have studied, greater the speed, greater is the momentum. When an accidents occurs, the greater momentum involved can cause greater damage.

1. http://outreach.phas.ubc.ca/phys420/p420_96/danny/danweb.htm ## Doubt in Law of Gravitation Newton's law of universal gravitation for two bodies. This law governs gravitational forces in the Earth. (Photo credit: Wikipedia) According to law of gravitation
F=g*(m1*m2)/r^2
If we bring two objects close to each other say our hands then the distance will be zero and the force of attraction will become infinite because r will we zero. Therefore F will become infinite but this is not the case.
When we touch our both palms together we can easily pull then away.

When we consider the distance, it is between the center of mass of the two bodies under consideration. When we bring our hands together the distance between their CM is not zero.

Other wise, the two particles under consideration must be point masses.

Then if you consider two atoms or two nuclei, the forces that come into play will be different if we decrease the distance between two atoms or nuclei. The attraction will turn into strong repulsion when the limits are exceeded. ## Form of Kepler’s in a different universe!

“imagine a planetary system in which gravitational force varied as 1/r instead of 1/r2 .what relation would correspond to KEPLER’S THIRD LAW (SQUARE OF TIME PERIOD / CUBE OF SEMI MAJOR AXIS.?”

If the gravitational force varied as 1/r instead of 1/r2 , then Kepler’s Law of periods would have to be modified accordingly and it would give T proportional to r.

## magnetic field

Which one we should use Bio saverts law or amperes law to find a magnetic field?

chirag

Both are used to find the magnetic field .In the case  of physical magnet Biot-Savarts law can be used

In the case of a current carrying conductor Ampers circuital law is used

## Do the super conductors obey the second law of thermodynamics?

Second law of thermodynamics is not violated.

If you can illustrate your idea and doubt, we may be able to discuss in more detail.

## Gauss`s law

“A circular ring of radius r made of a non conducting material is placed with its axis is parallel to a uniform electric field if the ring rotated by 180 degrees Does the flux changes? A Q charge is uniformly distributed on a thin spherical shell If a point charge is brought near it what is the field at the center?Is u r answer depends on whether it is conducting or non conducting?”

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