# Two parallel wires each of length 10 cm are 0.5 cm apart. A film of water is formed between them….

Q: Two parallel wires each of length 10 cm are 0.5 cm apart. A film of water is formed between them. If surface tension of water is 0.072 N/m, then the work done in increasing the distance between the wires by 1 mm is

(a) 1.44 × 10-5 J

(b) 1.72 × 10-5 J

(c) 1.44 × 10-4 J

(d) 1.72 × 10-4 J

Ans: (a)

Sol : $\displaystyle \Delta A = 2[10\times 10^{-2} \times 1 \times 10^{-3}]$

= 2 × 10-4 m2

W = S × ΔA

W = 0.072 × 2 × 10-4

= 0.144 × 10-4

= 1.44 × 10-5 J