JEE MAIN - Physics (2012 - No. 20)
A thin liquid film formed between a U-shaped wire and a light slider supports a weight of $$1.5 \times {10^{ - 2}}\,\,N$$ (see figure). The length of the slider is $$30$$ $$cm$$ and its weight negligible. The surface tension of the liquid film is
$$0.0125\,\,N{m^{ - 1}}$$
$$0.1\,\,N{m^{ - 1}}$$
$$0.05\,\,N{m^{ - 1}}$$
$$0.025\,\,N{m^{ - 1}}$$
Explanation
At equilibrium,
$$2Tl = mg$$
$$T = {{mg} \over {2l}} = {{1.5 \times {{10}^{ - 2}}} \over {2 \times 30 \times {{10}^{ - 2}}}} = {{1.5} \over {60}}$$
$$ = 0.025\,N/m = 0.025Nm$$
$$2Tl = mg$$
$$T = {{mg} \over {2l}} = {{1.5 \times {{10}^{ - 2}}} \over {2 \times 30 \times {{10}^{ - 2}}}} = {{1.5} \over {60}}$$
$$ = 0.025\,N/m = 0.025Nm$$
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