9)Aluminium-coated dewars are cylindrical flasks used to safely store and transport liquid nitrogen, dry ice etc. A company manufactures such dewars of different sizes. Shown here are two dewars, both of the same height but of different diameters. 

How much aluminium will be required to cover Dewar A compared to that required for Dewar B?
(Note: The base and the lid are NOT made up of aluminium.)

Dear Student,

Please find below the solution to the asked query:

Given : Diameter of Dewar A  =  30 cm so radius  of Dewar A =  15 cm

And

Diameter of Dewar B  =  10 cm so radius  of Dewar B =  5 cm

And height is same , So Height of Dewar A  =  Height of Dewar B  =  h cm

Base and lid are not made of aluminium , So

We know curved surface area of cylinder = 2 $\mathrm{\pi }$ rh  , So

Aluminium required to cover Dewar A  =  2 $\mathrm{\pi }$ ( 15 ) ( h ) =  30 $\mathrm{\pi }$ h   cm² 

And

Aluminium required to cover Dewar B  =  2 $\mathrm{\pi }$ ( 5 ) ( h ) =  10 $\mathrm{\pi }$ h   cm² 

Therefore,

Aluminium required to cover Dewar A  =  3 ( Aluminium required to cover Dewar B  )                               ( Ans )


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