Question

A water film is formed between the two straight parallel wires, each of length 10 cm, kept at a separation of 0.5 cm. Now, the separation between them is increased by 1 mm without breaking the water film. The work done for this is ______.

(surface tension of water = 7.2 x 10^-2Nm^-1)

विकल्प

• 1.44 × 10^-5 J

• 5.76 × 10^-5 J

• 7.22 × 10^-6 J

• 2.88 × 10^-5 J

Answer 1

A water film is formed between the two straight parallel wires, each of length 10 cm, kept at a separation of 0.5 cm. Now, the separation between them is increased by 1 mm without breaking the water film. The work done for this is 1.44 × 10^-5 J.

Explanation:

Increase in the area of the film is

ΔA = 10 cm × 0.1 cm = 1 cm² = 10^-4 m²

Work done W = 2 T.ΔA

= 2 × 7.2 × 10^-2 × 10^-4 J

= 1.44 × 10^-5 J