# A Wire Forming a Loop is Dipped into Soap Solution and Taken Out So that a Film of Soap Solution is Formed. a Loop of 6.28 Cm Long Thread is Gently Put on the Film - Physics

Short Note

A wire forming a loop is dipped into soap solution and taken out so that a film of soap solution is formed. A loop of 6.28 cm long thread is gently put on the film and the film is pricked with a needle inside the loop. The thread loop takes the shape of a circle. Find the tension the the thread. Surface tension of soap solution = 0.030 N m−1.

#### Solution

The loop will take circular shape after pricking. Raduis of which is given by the relation.

l =  2 (pi) R or R = 1/(2pi) = 6.28 / (2 xx 3.14) = 1 cm

=10-2 m

2T sin dθ force in inward direction is balanced by surface tension force in out ward dirction.

∴ 2T sin(θ) = ( surface tension ) × (length of are )

For small angles.  sin d(θ) = d(θ)

∴ 2Td(θ) = S(2Rdθ) (S = Surface tension)

∴ T = SR

=(0.020) (10-2 )

= 3.0 × 10-4 N.

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#### APPEARS IN

HC Verma Class 11, 12 Concepts of Physics 1
Chapter 14 Some Mechanical Properties of Matter
Q 29 | Page 301