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| To Measure the Distance of a Submarine (Echo Method) |
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Ultrasonic waves are transmitted through the ocean and if on its path any submerged objects are encountered, then as per law, the waves are reflected back to the origin. The time of sending the wave and the time of receiving the reflected wave are worked out and the distance of the submerged object (submarine in this case) is worked out by the
formula  where s is the distance between the point of transmission, v is the velocity of sound waves sent and t is the total time taken by the waves to travel to and fro. |
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| Time |
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| Time is measured by electrical oscillators, electronic oscillators, quartz and crystal clocks, atomic clocks, decay of elementary particles and radioactive dating. |
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