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MHT CET 2021 (22 Sep, Shift 1) · Thermometry & Thermal Expansion

Thermometry & Thermal Expansion question from MHT CET 2021 (22 Sep, Shift 1)

Q51MHT CET 2021 · 22 SEP · SHIFT 1Medium

Thermometry & Thermal Expansion

Let ' $\text{W}_1$ ' be the work done in blowing a soap bubble of radius ' $r$ ' from soap at room temperature. The soap is now heated and second soap bubble of radius ' $2r$ ' is blown from the heated soap solution. If ' $W_2$ ' is the work done in forming this bubble then

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Answer: (d)

Work to blow a bubble $W = 8\pi r^2 T$ (two surfaces).
At radius $2r$ with the same $T$ it would be $4W_1$ .
Surface tension decreases on heating, so $T' < T$ .
So $W_2 < 4W_1$ , answer (d).

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