Question

Assertion : Current is passed through a metallic wire, heating it red. When cold water is poured on half of it, the rest becomes more hot.
Reason : Resistance decreases due to the decrease in temperature and then current through wire increases.

• A. Both (A) and (R) are true and (R) is the correct explanation of A
• B. Both (A) and (R) are true but (R) is not the correct explanation of A
• C. (A) is true but (R) is false
• D. (A) is false but (R) is true

Answer 1

Answer: (A)

Both (A) and (R) are true and (R) is the correct explanation of A

$\alpha$ of the metal is $+ve$ so when its temperature is reduced by pouring water, its resistance also decreases leading to increase in the amount of power liberated through it there by heating.

because voltage applied is constant therefore the relation between power liberated and resistance is :

$P=\frac{V^2}{R}$

so $P\propto \frac{1}{R}$

that's why due to decrease in resistance the power liberated increases and it appears as more heating in metal.