A water film is formed between two straight parallel wires of 10 cm length 0.5 cm apart. If the distance between wires is increased by 1 mm. What will be the work done? (surface tension of water =72 dyne / cm )

Question

A water film is formed between two straight parallel wires of 10 cm length 0.5 cm apart. If the distance between wires is increased by 1 mm. What will be the work done? (surface tension of water =72 dyne / cm ) (A) 36 erg (B) 288 erg (C) 144 erg (D) 72 erg

Tardigrade Admin · Accepted Answer

Work done = Surface tension × increase in area of the film W = S × Δ A Increase in area = Final area - initial area =10 ×(0.5+0.1)-10 × 0.5=1 cm 2 ∴ W =72 × 2 × 1=144 erg [ ∵ There are 2 free surfaces; ∴ Δ A =2 × 1].

Q. A water film is formed between two straight parallel wires of $10 c m$ length $0.5 c m$ apart. If the distance between wires is increased by $1 mm$ . What will be the work done?
(surface tension of water $= 72 d y n e / c m$ )

$36 er g$

$288 er g$

$144 er g$

$72 er g$

Work done $=$ Surface tension $\times$ increase in area of the film
$W = S \times Δ A$
Increase in area $=$ Final area $-$ initial area
$= 10 \times (0.5 + 0.1) - 10 \times 0.5 = 1 c m^{2}$
$∴ W = 72 \times 2 \times 1 = 144 er g$
[ $∵$ There are $2$ free surfaces; $∴ Δ A = 2 \times 1]$ .

Q. A water film is formed between two straight parallel wires of 10cm length 0.5cm apart. If the distance between wires is increased by 1mm. What will be the work done? (surface tension of water =72dyne/cm )

36erg

288erg

144erg

72erg