A glass bulb is balanced by a brass weight in a sensitive beam balance. Now the balance is covered by a glass-jar which is then evacuated. Then:
A
the beam will remain horizontal
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B
the pan containing the bulb will go down
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C
the pan containing the bulb will go up
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D
none of the above
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Solution
The correct option is B the pan containing the bulb will go down
When the glass bulb is weighed by a brass weight in air both of them displaces air, but the glass bulb being of much larger volume displaces larger volume of the air. when the system is covered by a bell jar. which is then evacuated the upthrust due to displaced air will be absent and the glass bulb will weigh more. thus, pen with the bulb goes down