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Monthly Archives: December 2011


Vibration of ferromagnet

Why a ferromagnet vibrates in a alternating magnetic field?
(Swadipriya asked this)

Questions received and waiting to be answered

Sreeda Asks

  1. Why are we not feeling Earth’s rotation while it is actually happening {1674.4 km/hr at the equator}?
  2. Our sound varies while communicating through a telephone. Why?
  3. Why is it more neat when we tear a sheet from the newspaper vertically and rough when torn horizontally?
  4. Will we be able to see stars during day time on the moon?
  5. Why do planets move in elliptical paths and not in circular ones?
  6. At what depth do Jupiter quakes occur?
  7. Charan Asks

what is the difference between a atomic and a nuclear bomb?

sly nikie asks

what is crystal cleavage and what does it state about the nature of matter?

A Numerical from Kinematics

Pooja asked:

an aeroplane flies 400km due west from city A to city B,then 300km north east to city C,and finally 100km north to city D. how far is it from city A to D?in what direction must the aeroplane had to return directly to city A from city D?

Answer will be posted soon

Electromagnetic Induction – Direction of Induced Current

I am unable to understand “How to find the direction of induced current?” please help me and explain me all the steps, how to do it? (Saroj Sharma asks)


Lenz’s Law states that the direction of induced current is such that it opposes the cause which produced it.


If the south pole of  a magnet is brought near a coil, induced emf is induced in it. According to Lenz’s law, the induced current should oppose the south pole. Therefore the direction of induced current will be clockwise as seen from the magnet producing a south pole repelling the approaching magnet.

Fleming’s Right Hand Rule

Fleming's Right Hand Rule Direction of Induced CurrentFleming’s Right Hand Rule states that if we stretch the Thumb, Forefinger and Central Finger of right hand in mutually perpendicular directions in such a way that Thumb shows the direction of motion of a  conductor, forefinger shows the direction of magnetic field, then the central finger shows the direction of induced current.

(While solving problems, please remember that the direction of current is opposite to the direction of flow of electrons, by convention)



Light Year

A Light Year is the distance travelled by light in vacuum in one year. How many metres are there in one light year?  (Noor asked)


Speed of light in vacuum is 3 x 108 m/s

1 year = 365 days = 365 x 24 hours=365 x 24 x 60 minutes = 365 x 24 x 60 x 60 seconds

We know that distance = speed x time


1 LY = 3 x 108 x 365 x 24 x 60 x 60 m = 9.460528405×1015 m

Cable transmission of signals

HS Varun asked:

How is it possible to transmit a no. of channels through the same cable ?
Is it based on the concept of Bandwidth ?


In a cable TV system, each channel is assigned a range of frequency (6-8MHz range)

A problem from Dynamics

The coefficient of kinetic friction between the 2.00-kg and 3.00-kg blocks
is 0.300. The horizontal surface and the pulleys are frictionless, and the masses are released from rest.
a) Draw a free-body diagram for each block.
b) Determine the acceleration of each block.
c) Find the tension in the strings.

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