Drop a hot coin into a cup of water and the water warms up a little. Melt an ice cube on your palm and it feels cold for a surprisingly long time. Both are heat moving from one object to another. Calorimetry is the branch of physics that measures exactly how much heat that is.
MCQ Questions🏛️ Must Know
What Calorimetry Measures
- Calorimetry Calorimetry is the science of measuring heat. It tracks the energy transferred between objects at different temperatures.
- Units Heat is measured in joules (J), the SI unit. An older unit, the calorie, still appears in many numerical problems.
- One Calorie One calorie raises 1 gram of water by 1°C. It equals about 4.186 joules.
- Specific Heat Specific heat capacity, c, is the heat needed to raise 1 kg of a substance by 1°C. The formula is Q = mcΔT.
- Water's Value Water's specific heat is 4186 J/(kg·K), or 1 cal/g°C. This is unusually high, which is why large water bodies warm and cool slowly.
📘 Good to Know
Heat Capacity and Latent Heat
- Heat Capacity Heat capacity is the total heat needed to raise an object's full mass by 1°C. It equals mass times specific heat, S = mc.
- Water Equivalent A real calorimeter absorbs some heat too. Its "water equivalent" is the mass of water that would need the same heat, and it gets added into the balance equation.
- Latent Heat Latent heat is the heat absorbed or released during a change of state. Temperature stays constant while this heat is exchanged.
- Fusion Ice's latent heat of fusion is about 334 J/g, or 80 cal/g. It is the heat needed to melt ice at 0°C.
- Vaporization Water's latent heat of vaporization is about 2260 J/g, or 540 cal/g. It is far higher than fusion, because turning liquid into gas breaks many more molecular bonds.
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🌟 Great to Know
The Principle of Calorimetry and Joule's Discovery
- The Principle In an isolated system, heat lost by a hotter body equals heat gained by a cooler body. This follows from the law of conservation of energy.
- The Calorimeter A calorimeter is an insulated vessel with a stirrer and thermometer. It stops heat escaping to the surroundings during a measurement.
- Common Trap A body changing phase, like melting ice, needs its latent heat added first. Skipping this step, before applying specific heat, is the most common calorimetry mistake.
- Joule's Experiment James Prescott Joule's 1840s paddle-wheel experiments showed that heat and mechanical work are the same kind of energy. A falling weight turned a paddle inside insulated water, and friction warmed the water.
- The Constant Joule's result gave the mechanical equivalent of heat, about 4.186 joules per calorie. It is the same conversion figure calorimetry sums use today, and it helped establish the first law of thermodynamics.
📝 Exam Point of View
NDA & NA (I) 2026 GAT — Two Calorimetry Questions
- Question NDA & NA (I) 2026, General Ability Test, Q53 gave a solid whose specific heat varies with temperature, C(T) = C0 + αT. It asked for the heat released on heating from T1 to T2. The correct answer is Q = m(T2 − T1)[C0 + (α/2)(T1 + T2)].
Why The trap is using Q = mCΔT directly, which only works when specific heat stays constant. Here C changes with temperature, so the heat comes from integrating C(T) over the range, not from one plugged-in value.
Link See the full question, NDA & NA (I) 2026 GAT, Q53. - Question NDA & NA (I) 2026 GAT Q61 asked how much water at 30°C is needed to melt 5 g of ice at −20°C, so the final mixture sits at exactly 0°C liquid. The correct answer is 0.015 kg.
Why The trap is skipping the step where the ice first warms from −20°C to 0°C, before it melts. That step needs the specific heat of ice (0.5 cal/g°C), on top of its latent heat of fusion (80 cal/g).
Link See the full question, NDA & NA (I) 2026 GAT, Q61.
NDA-NA-2 2017 — Heat Cannot Flow Uphill on Its Own
- NDA-NA-2 2017 Asked what names the rule that heat cannot flow by itself from a colder body to a hotter one. The answer is the second law of thermodynamics, the Clausius statement -- moving heat the other way needs external work, as in a refrigerator. Test yourself on this question
- NDA & NA (I) 2025 GAT Asked what a system with no heat exchange with its surroundings is called. The answer is an adiabatic system, thermally insulated so any temperature change comes only from work, not heat transfer. Test yourself on this question
- NDA & NA (II) 2025 GAT Asked what the heat needed to change unit mass of a substance from liquid to vapour without a temperature change is called. The answer is specific latent heat. Test yourself on this question
CAPF (ACs) 2025 — The Refrigerator's Working Principle
- Question CAPF asked which principle the refrigerator's working is based on. The correct answer is the second law of thermodynamics.
Why A refrigerator pumps heat from its cold interior to the warmer room outside, which does not happen on its own by the second law -- external work (the compressor) is needed to force it.
Link See the full question, CAPF (ACs) 2025, Q109.
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