Question

A wire of length 20 cm is placed horizontally on the surface of water and is gently pulled up with a force of $1.456 \times 10^{-2}\, N$ to keep the wire in equilibrium. The surface tension of water is

• A. \(0.00364\, N/m\)
• B. \(0.0364\, N/m\)
• C. \(0.00464\, N/m\)
• D. \(0.0864\, N/m\)

Hint:

Surface tension force acts along both sides of the wire; hence total length considered is twice the length of the wire.

Answer 1

The Correct Option is B

Surface tension \(T\) is force per unit length. For a wire with two surfaces in contact with water: \[ T = \frac{F}{2L} \] Given: \[ F = 1.456 \times 10^{-2} N, \quad L = 20\, \text{cm} = 0.2\, m \] Calculate: \[ T = \frac{1.456 \times 10^{-2}}{2 \times 0.2} = \frac{1.456 \times 10^{-2}}{0.4} = 0.0364\, N/m \]