Physics
A wavelength of 0.3 m is produced in air and it travels at a speed of 300 m/s. Then it will be an

Audible wave
Microwave
Infrasonic wave
Ultrasonic wave

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Physics
Light houses are places with powerful lights to :

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

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