Question

A U-shaped wire is dipped in a soap solution and removed. The thin soap film formed between the wire and light slider supports a weight of \( 1.5 \times 10^{-2} \, \text{N} \). The length of the slider is 30 cm. What is the surface tension of the film?

• A. \( 3 \times 10^{-3} \, \text{N/m} \)
• B. \( 2 \times 10^{-5} \, \text{N/m} \)
• C. \( 4 \times 10^{-4} \, \text{N/m} \)
• D. \( 2.5 \times 10^{-2} \, \text{N/m} \)

Hint:

For a soap film, the surface tension can be found by dividing the weight supported by the film by twice the length of the wire.

Answer 1

The Correct Option is D

The tension in a soap film can be calculated using the following formula: \[ T = \frac{W}{2l} \] where \( W = 1.5 \times 10^{-2} \, \text{N} \) is the weight supported by the film and \( l = 30 \, \text{cm} = 0.3 \, \text{m} \) is the length of the slider. Substituting the values: \[ T = \frac{1.5 \times 10^{-2}}{2 \times 0.3} = 2.5 \times 10^{-2} \, \text{N/m} \]
Thus, the correct answer is (d).