8(b)
(i) What are superconductors?
(ii) Calculate the current drawn by an appliance rated 110 W, 220 V when connected across 220 V supply.
(iii) Name a substance whose resistance decreases with the increase in temperature.
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(i) A superconductor is a substance of zero resistance (or infinite conductance) at a very low temperature.
(ii) For the given appliance, W = 110 W, V = 220 V
$\therefore \text{Current I} = \frac{W}{V} = \frac{110}{220} = 0.5 \text{ A}$
Hence, current drawn by the appliance = 0.5 A
(iii) The resistance of semi conductors such as carbon, silicon, etc., decreases with increase in temperature.