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why do electrostatics experiments not work well on humid days?

Humid air contains water droplets and make it conducting. Humid air defects static electricity experiments in two ways,

(1) It reduces friction

(2) It carries away the charges on rubbed bodies.

Potential Difference

Pawan Asked

“What is meant by potential difference?”


“Potential Difference between two points is the difference in Potential between the two points and is equal to the work done per unit charge ion carrying a positive test charge from one point to another against the electric field and without any acceleration”

Working of a microphone

How does a microphone do its work? Please explain me and can you give me answer in language Hindi I’m very thankful to you. (Shubham Agnihotri asked)

inside a microphone
Microphone is a transducer (a device which converts energy from one form to another). The microphone converts sound energy to mechanical energy and then to electrical energy.

When we speak into the mic, the vibrations of the air produced by the sound make the diaphragm of the mic vibrate. A coil attached to the diaphragm vibrates together with it. The coil is moving in a strong magnetic field produced by a permanent magnet. Whenever the magnetic flux linked with coil changes an emf is induced in it. Therefor when we speak into the mic, an emf varying similar to the pressure variations produced by our sound is produced across the coil by electromagnetic induction.

If the ends of the coil is connected to an amplifier this can be amplified and can be send to the loudspeaker. The working of the loudspeaker is just the reverse of that of the microphone. I converts the electrical signal to sound signals.

(Please use Google Translate  or Click Here to get the Hindi Version)

Conservation of Angular Momentum and Kinetic Energy

Imagine a rod 2 meters long fixed at its center, 2 identical masses are placed 0.5 meters away on opposite sides , as the rod spins they slide towards the edges , according to the formula k.E.=0.5*I*ω2 the kinetic energy decreases , but since its a closed system why does the kinetic energy decrease ?



The decrease in KE accounted by the work done in displacing the masses

Heating up of water due to shaking

Would shaking a bottle of chilled water, cause it to warm up, even slightly, due to some kind of friction?


Shaking BottleYes, This is due to friction (Viscous forces). The different layers of water resist relative motion and the work done in producing motion against the viscous force appears  as heat.

Preparing for IIT JEE Physics

Yudhvir asks: “Hello Sir!!! I m in 11th!! I want to do less work & more benefit!! I don’t like to study at all!!…but i have decided to do only DC Pandey!! is it enough for IIT preparation???”


Answer: No pain, no gain!

Whatever be the book you follow, understanding the basic concepts is all the most important. Make sure that you can solve all the solved and unsolved exercise in CBSE text book. These questions are originally set by a group of experts who are also among the question paper setters for IIT JEE. If you can solve the NCERT text book problems with ease, you have acquired the required standard. Then you may take up any book for solving additional problems.

If you have any doubt, feel free to ask here.

Best if luck!

Misconception on Work and energy conservation

It is said that when work is done energy is lost. But when a man runs in a circular path and reaches the starting point, then the work done is zero but energy is lost. (Divyam asked)
Answer: The work done here is not zero, work is done and energy is spent to overcome friction. Though he is reaching the same point, he is moving against a non conservative force, friction (where the work done in a closed path is not zero)

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