CDS Physics · Free notes

Heat: CDS Physics

Heat and Thermodynamics has 13 past-year questions in CDS General Knowledge, from 2017 (II) to 2026 (I): 5 EASY, 6 MODERATE and 2 HARD. Five of them describe something you have seen at home, such as a pot of boiling water, a bowl of hot rice or a cotton shirt in summer, and ask which idea explains it. None needs a calculation: the three temperature questions ask for the conversion formula itself. So learn the three ways heat travels and what latent heat does, keep the two conversion formulas exact, and read every option against the everyday case in the stem.

The handout has every subtopic, worked example, formula and trap with answers shown. The formula sheet is the chapter’s formulas and traps alone, on one page.

CDS home All formulas on one page

Subtopic notes

Formula & revision sheet

3 formulas · 2 reference tables · 10 gotchas across all subtopics — the exam-eve cheat-sheet

Temperature and Heat Transfer

Formulas (2)

Temperature scales: Kelvin, Celsius and Fahrenheit · Converting between temperature scales $T = t_C + 273.15 \qquad T_F = \tfrac{9}{5}\,T_C + 32 \qquad T_C = \tfrac{5}{9}\,(T_F - 32)$
Specific heat and the principle of calorimetry · Heat for a temperature change, and the calorimetry balance $Q = m\,c\,\Delta T \qquad m_1 c_1 (T_1 - T) = m_2 c_2 (T - T_2)$

Reference tables (1)

Conduction, convection and radiation8 rows

Everyday case	Main mode of heat transfer
Heating one end of a brass rod warms the other end	Conduction
Water boiling in a pot on a gas stove	ConvectionQ CDS 2024 (II): boiling water in a pot is the example of convection.
Land and sea breezes	Convection
Warm air circulating round a blast furnace	Convection
Feeling the warmth of the Sun	Radiation
Glass of an electric bulb heated by the glowing filament	RadiationQ CDS 2018 (II): this is the one case in a list that is not convection.
Thermal conductivity, highest to lowest	Copper, aluminium, water, hydrogen gasQ CDS 2026 (I): hydrogen gas has the least thermal conductivity of these four.
Cooling a hot bowl of rice fast	Stand it in water and run a fan at full speedQ CDS 2024 (I): a water bath with a fast fan beats still air, a cooled room or water alone.

Watch out for (6)

Add 273 to go from Celsius to Kelvin, never subtract
→ Temperature scales: Kelvin, Celsius and Fahrenheit
The Fahrenheit constant is 32, and the factor is 9/5
→ Temperature scales: Kelvin, Celsius and Fahrenheit
A microwave oven does not heat by convection
→ Conduction, convection and radiation
Every gas is a poor conductor, even the best one
→ Conduction, convection and radiation
Radiation needs no medium; conduction and convection do
→ Conduction, convection and radiation
Calorimetry and thermal equilibrium are not the same name
→ Specific heat and the principle of calorimetry

Change of State and Gases

Formulas (1)

Latent heat, evaporation and the triple point · Heat for a change of state $Q = m\,L$

Reference tables (1)

The ideal gas and thermodynamic processes5 rows

Process	What stays constant
Isothermal	Temperature
Isobaric	Pressure
Isochoric	Volume
Adiabatic	No heat flows in or out of the gas
Joule-Thomson throttling	Enthalpy (an isoenthalpic process)

Watch out for (4)

Latent heat changes the state, not the temperature
→ Latent heat, evaporation and the triple point
The triple point is 273.16 K, not 273.15 K or 0 K
→ Latent heat, evaporation and the triple point
Equal average energy does not mean equal speeds
→ The ideal gas and thermodynamic processes
Isochoric is volume, isobaric is pressure
→ The ideal gas and thermodynamic processes

PYQ weightage by concept

5 concepts · 13 PYQs — where the marks actually sit, so you know what to drill first

Temperature and Heat Transfer8 PYQs · 62%

Concept	PYQs	Share
Conduction, convection and radiation	4	31%
Temperature scales: Kelvin, Celsius and Fahrenheit	3	23%
Specific heat and the principle of calorimetry	1	8%

Change of State and Gases5 PYQs · 38%

Concept	PYQs	Share
Latent heat, evaporation and the triple point	3	23%
The ideal gas and thermodynamic processes	2	15%

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