AP EAPCET 07-Jul-2022 Shift 2 Paper

If radius (r) of a circle made two times (2r) then change in area =π(2r)2−πr2
=3πr2=3×‌ initial area ‌
Here, initial area of soap film, A1=10cm2
Final area has a radius twice that of initial radius.
So, change in area △A=3A1=3×10cm2
=3×10×10−4m2
=3×10−3m2
As, a liquid film has two surfaces (one top and other bottom).
Change in surface energy or work done,
W=2△A×T
T= Surface tension
or T=W∕2△A
Here, W=8×10−3J
∆A=30×10−3m2
So, surface tension of Liquid, T=

8×10−3

2×3×10−3

=

8

6

=‌

4

3

=1+

1

3

Nm−1
Hence, α=3