Physics · Properties of bulk matter · chapter 10 of 14

Class 11 Physics Chapter 10: Thermal Properties of Matter Assertion-reason questions with answers

2 assertion-reason questions on Thermal Properties of Matter, each with its answer and the reason, written from the NCERT chapter. For school exams on the CBSE pattern, JEE Main and NEET, which are set from the same NCERT chapter. Open a question's solution to check your working; then take the free test to find your next chapter. Each question gives an Assertion (A) and a Reason (R); choose how they stand to each other.

Question 1
Assertion (A): A pond in a cold region freezes first at its surface. Reason (R): Water has its maximum density at 4 °C, and water colder than this is less dense.
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Answer: (a) Both A and R are true, and R is the correct explanation of A.

Both are true. As the pond cools, water near 4 °C sinks; once the top layer falls below 4 °C it is less dense, stays at the surface and freezes there. The density maximum at 4 °C is exactly why the freezing starts at the top, so R explains A.

Question 2
Assertion (A): The bottoms of cooking utensils are often blackened. Reason (R): Copper is a good conductor of heat, and some cooking pots have a copper coating on the bottom.
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Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Both are true. The bottoms are blackened because black surfaces absorb the most radiant heat from the fire. R is about conduction spreading the heat over the base of a copper-bottomed pot; it does not explain the blackening.

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