Physics
Optical fibre works on the

total internal reflection
scattering
interference
principle of refraction

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Physics
Light houses are places with powerful lights to :

Guide and resolve traffic jams in crowded metro-cities during nights
Guide and warn the ships coming from different directions in the ocean
Indicate to the incoming warships, the location of a harbour during night
Guide and help large crowds at religious gathering during nights

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Physics
When a pail of water is swung in a vertical circle, the water does not fall out at the top of the loop when the speed is

Above a certain minimum value irrespective of amount of water in the pail
Below a certain minimum value depending on amount of water in the pail
Above a certain minimum value depending on amount of water in the pail
Below a certain minimum value irrespective of amount of water in the pail

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