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Latent Heat and Phase Transitions

Problems and explanations focused on energy involved in melting, freezing, boiling, and condensation. Helps students grasp phase change concepts in thermodynamics.

25 questions

Latent Heat and Phase Transitions

A copper plate has an area of 0.8m2 at 60∘C. What is the decrease in area when cooled to 10∘C? (αl\=1.7×10−5K−1)

Given: A0 = 0.8m2, ΔT = 10−60 = −50∘C, αl = 1.7×10−5K−1. ΔA = A0×2αlΔT = 0.8×2×1.7×10−5×(−50). ΔA = 0.8×3.4×10−5×(−50) = −0.00136m2 (decrease of 0.00136m2). As per NCERT, applying relevant law/formula with correct units and sign convention leads to 0.00136 m². This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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Latent Heat and Phase Transitions

A 0.3kg lead block at 350∘C is placed in 0.6kg water at 25∘C. Find the final temperature. (Specific heat of lead = 127.7

0.3×127.7×(350−T) = 0.6×4186×(T−25). 13408.5−38.31T = 2511.6T−62790. 13408.5+62790 = 2511.6T+38.31T. 76198.5 = 2549.91T⇒T≈29.89∘C≈29.9∘C. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 29.9°C. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCERT Class 11 Physics, Chapter 11: Thermal Properties – Calorimetry.

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Latent Heat and Phase Transitions

Which substance typically has the highest specific heat capacity among common materials?

Water has the highest specific heat capacity (4186J kg−1K−1) among common substances listed (Section 10.6, Table 10.3), making it an effective coolant. As per NCERT, applying relevant law/formula with correct units and sign convention leads to Water. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCERT Class 11 Physics, Chapter 11: Thermal Properties – Calorimetry.

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Latent Heat and Phase Transitions

A silver ring has an inner circumference of 31.4cm at 15∘C. What temperature must it be heated to for the circumference

Given: L0 = 31.4cm, ΔL = 0.0597cm, αl = 1.9×10−5K−1, T1 = 15∘C. ΔL = L0αlΔT⇒0.0597 = 31.4×1.9×10−5×ΔT. ΔT = 0.059731.4×1.9×10−5 = 0.05975.966×10−4≈100K. T2 = 15+100 = 115∘C. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 115°C. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: NCERT Class 11 Physics, Chapter 11: Thermal Properties – Calorimetry.

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Latent Heat and Phase Transitions

Which temperature scale uses 32∘ and 212∘ as the freezing and boiling points of water at standard pressure?

The Fahrenheit scale defines the freezing point of water as 32∘F and boiling point as 212∘F at standard pressure (Section 10.3). As per NCERT, applying relevant law/formula with correct units and sign convention leads to Fahrenheit. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: NCBI Bookshelf, Ideal Gas Law: P1V1/T1 = P2V2/T2.

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Latent Heat and Phase Transitions

How much heat is required to raise the temperature of 2kg of water from 20∘C to 50∘C? (Specific heat capacity of water =

Given: m = 2kg, ΔT = 50−20 = 30∘C, s = 4186Jkg−1K−1. Heat required: ΔQ = msΔT = 2×4186×30 = 251160J. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 251.16 kJ. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCERT Class 11 Physics, Chapter 11: Thermal Properties – Calorimetry.

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Latent Heat and Phase Transitions

Why do gases expand more than solids for the same temperature increase?

Gases have a much higher coefficient of volume expansion than solids due to weaker intermolecular forces, allowing greater volume changes with temperature. As per NCERT, applying relevant law/formula with correct units and sign convention leads to Gases have a higher expansion coefficient. This satisfies dimensional consistency and physical conditions given, so option D is scientifically correct.

Ref: NCBI Bookshelf, Ideal Gas Law: P1V1/T1 = P2V2/T2.

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Latent Heat and Phase Transitions

A 0.15kg aluminium block at 280∘C is placed in 0.7kg water at 22∘C in a 0.05kg lead calorimeter at 22∘C. What is the fin

0.15×900×(280−T) = (0.7×4186+0.05×127.7)×(T−22). 37800−135T = (2930.2+6.385)×(T−22) = 2936.585T−64599.87. 37800+64599.87 = 2936.585T+135T. 102399.87 = 3071.585T⇒T≈33.34∘C≈33.3∘C. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 33.3°C. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: NCERT Class 11 Physics, Chapter 11: Thermal Properties – Calorimetry.

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