JEE MAIN - Physics (2021 - 17th March Morning Shift - No. 7)
When two soap bubbles of radii a and b (b > a) coalesce, the radius of curvature of common surface is :
$${{b - a} \over {ab}}$$
$${{a + b} \over {ab}}$$
$${{ab} \over {a + b}}$$
$${{ab} \over {b - a}}$$
Explanation
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$${P_1} - {P_0} = {{4S} \over b}$$ ....(1)
$${P_2} - {P_0} - {{4S} \over a}$$ .....(2)
$${P_2} - {P_1} = {{4S} \over R}$$ ......(3)
eq(2) - eq(1) = eq(3)
$$ \Rightarrow $$ $${1 \over a} - {1 \over b} = {1 \over R}$$
$$ \therefore $$ $$R = {{ab} \over {b - a}}$$
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