Question

# An electric bell is suspended in an airtight vacuum jar. The bottom of the jar is connected to an air pump, as shown in the given figure. The air pump can fill air in the jar. What will happen when the switches of both the bell and the pump are pressed? The jar will break into pieces There will be a gradual decrease in the intensity of the sound There will be a gradual increase in the intensity of the sound A spark will be produced in the bell

Solution

## The correct option is C There will be a gradual increase in the intensity of the sound Sound cannot travel in vacuum. Hence, when there is no air in the jar, no sound will be heard. When the switches of both the air pump and the bell are pressed, the jar will slowly be filled with air. The presence of air inside the jar will cause the sound of the bell to travel through the jar. Hence a feeble sound will be heard. As more air passes into the jar, the intensity of the sound will increase gradually. The intensity of the sound will be the maximum when the jar will be completely filled with air.

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