Thermal Properties of Matter — Class 11 MCQs with Answers

Thermal Properties of Matter — important questions & MCQs with answers (Class 11 Physics)

6 solved questions from this chapter's difficulty levels, each with its answer and explanation. Tap an option to check yourself.

0 of 6 answered

1. Q1 of 6Easy

   0°C in Kelvin:

   A0 KB273.15 KC100 KD−273 K
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   Answer: 273.15 K

   Explanation: Kelvin scale: K = °C + 273.15, so 0°C = 273.15 K exactly. 0 K is absolute zero (−273.15°C), the tempting wrong pick since it swaps the roles of 0°C and 0 K.

2. Q2 of 6Easy

   Heat transfer through vacuum is by:

   AConductionBConvectionCRadiationDAll three
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   Answer: Radiation

   Explanation: Conduction needs a solid medium and convection needs a fluid to carry matter, but radiation is electromagnetic waves needing no medium — the only mode that crosses vacuum, like sunlight reaching Earth.

3. Q3 of 6Medium

   30°C = ? K

   A373B243.15C273D303.15
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   Answer: 303.15

   Explanation: K = °C + 273.15, so 30°C = 30 + 273.15 = 303.15 K. Subtracting 30 from 273.15 instead of adding gives the wrong 243.15 K.

4. Q4 of 6Medium

   Rod of length 1 m, α = 1.2 × 10⁻⁵ /°C. Expansion when heated 100°C:

   A0.12 mmB1.2 cmC1.2 mmDCannot compute
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   Answer: 1.2 mm

   Explanation: Linear expansion: ΔL = αL₀ΔT = 1.2×10⁻⁵ × 1 × 100 = 1.2×10⁻³ m = 1.2 mm. Misplacing the decimal gives the tempting 1.2 cm or 0.12 mm — a factor-of-10 slip is the trap here.

5. Q5 of 6Hard

   Heat to melt 1 kg ice at 0°C, heat the water to 100°C and vaporize it (L_f = 80 cal/g, c_water = 1 cal/g°C, L_v = 540 cal/g):

   A720,000 calB100,000 calC800,000 calD620,000 cal
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   Answer: 720,000 cal

   Explanation: Total heat sums three stages for 1 kg: melting (80×1000 cal), warming water 0→100°C (100×1000 cal, since c_water=1 cal/g°C), and vaporizing (540×1000 cal), giving 720,000 cal total.

6. Q6 of 6Hard

   Mixing 100 g ice at 0°C with 200 g water at 50°C. Final state (L_f = 80 cal/g, c_w = 1):

   AAll water at 33°CBAll water at ≈6.7°CCMixture of ice and water at 0°CDAll water at 0°C
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   Answer: All water at ≈6.7°C

   Explanation: The 200 g of water cooling 50°C releases 200×1×50 = 10000 cal, while melting all 100 g of ice needs only 100×80 = 8000 cal. So every gram melts and the surplus 2000 cal warms the 300 g of water by 2000/300 ≈ 6.7°C. Ignoring the latent heat entirely gives the tempting 33°C.

Thermal Properties of Matter notes: key concepts (Class 11 Physics)

Heat as energy in transit and its effects: temperature scales, linear, areal and volumetric expansion, specific and latent heat, the calorimetry principle for mixtures, and the three modes of heat transfer with the laws that govern conduction, Stefan-Boltzmann radiation and Newton's cooling.

Heat and temperature

Temperature measures the average kinetic energy of molecules and decides the direction of heat flow; heat is the energy actually in transit because of a temperature difference.

Temperature scales

Celsius, Fahrenheit and the absolute Kelvin scale. A change of one kelvin equals a change of one degree Celsius, so the two agree on differences but not on values.

Absolute zero

0 K, the temperature at which molecular motion is minimum. It is the natural zero of the Kelvin scale and cannot be reached in practice.

Linear expansion

A solid rod lengthens in proportion to its original length and the temperature rise, the constant being the coefficient of linear expansion α.

Areal and volume expansion

For an isotropic solid the areal coefficient is about 2α and the volumetric coefficient about 3α, since expansion happens along every dimension at once.

Anomalous expansion of water

Between 0 °C and 4 °C water CONTRACTS on heating, reaching maximum density at 4 °C. This is why lakes freeze from the top and aquatic life survives beneath.

Specific heat capacity

The heat needed to raise unit mass through one degree. Water's unusually high value of 4186 J kg⁻¹ K⁻¹ makes it an excellent coolant.

Thermal capacity

The heat needed to raise the temperature of a whole body by one degree, equal to mass times specific heat. It is a property of the object, not the material.

Latent heat

The heat absorbed or released during a change of state at CONSTANT temperature, going entirely into breaking or forming molecular bonds.

Latent heat of fusion and vaporisation

For water, 334 J g⁻¹ to melt ice and 2260 J g⁻¹ to boil water. The vaporisation value is far larger, which is why steam burns are so severe.

Calorimetry principle

In an isolated system the heat lost by hot bodies equals the heat gained by cold ones. Every mixture problem is this single equation.

Conduction

Heat transfer by molecular vibration and free electrons without bulk movement of matter — the dominant mode in solids, especially metals.

Thermal conductivity

The material constant in the conduction law. Metals have high values, while air, wool and cork are poor conductors and therefore good insulators.

Convection

Heat transfer by the actual movement of a heated fluid, which becomes less dense and rises. It explains sea breezes, land breezes and boiling.

Radiation

Heat transfer by electromagnetic waves, needing NO medium at all — the only mode by which the Sun's energy reaches the Earth across empty space.

Newton's law of cooling

For a small temperature excess, the rate of cooling is proportional to the difference between the body's temperature and its surroundings.