Physics
The quality or tone of a musical sound produced by a stringed instrument depends on

Length of the strings in the instrument
Amplitude of vibration
Frequency of vibration
Wave form of the sound

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Physics
Railway tracks are banked on curves so that

Necessary centrifugal force may be obtained from the horizontal component of the weight of the train
No frictional force may be produced between the tracks and the wheels of the train
Necessary centripetal force may be obtained from the horizontal component of the weight of the train
The train may not fall down inwards

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Physics
What is refractive index ?

None of above
It is defined as the ratio of speed of light in the medium to the speed of light in vacuum.
It is defined as the ratio of speed of light in vacuum to the speed of light in the medium.
It is defined as the product of speed of light in medium and in vacuum.

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