Physics
A decibel is

A musical instrument
A measure of sound level
A musical note
The wavelength of noise

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Physics
The sensation of weightlessness in a spacecraft in an orbit is due to the

Fact that spacecraft in the orbit has no energy
Presence of gravity outside but not inside the spacecraft
Acceleration in the orbit which is equal to the acceleration due to gravity outside
Absence of gravity outside

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Physics
A transformer

Is used to decrease or increase AC voltage
Converts DC to AC
Converts AC voltage to D.C. voltage
Converts electrical energy into mechanical energy

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