Topic 4 of 7Aga Khan Board

Heat & Thermodynamics

Temperature, heat transfer, specific heat capacity and change of state

Temperature measures how hot something is (°C or K). Heat is thermal energy transferred between objects (joules).

Kelvin = Celsius + 273. Absolute zero = 0 K = −273°C.

Heat transfer methods:

Conduction: Through solids. Particles vibrate and pass energy along. Metals are good conductors. Non-metals and air are insulators.

Convection: In fluids (liquids and gases). Hot fluid rises (less dense), cold fluid sinks → convection current.

Radiation: Electromagnetic waves (infrared). No medium needed — travels through vacuum. Dark, matt surfaces absorb and emit best. Shiny, light surfaces reflect/emit least.

Specific heat capacity (c): Energy needed to raise 1 kg by 1°C.

Q = mcΔT (Q = heat energy, m = mass, c = SHC, ΔT = temperature change).

Water has high SHC (4200 J/kg°C) — good coolant and climate regulator.

Changes of state:

Melting (solid→liquid), Boiling (liquid→gas) — absorb energy

Freezing (liquid→solid), Condensing (gas→liquid) — release energy

Latent heat = energy for change of state at constant temperature

Key Points to Remember

1Conduction in solids; convection in fluids; radiation needs no medium
2Q = mcΔT for temperature change
3Dark matt surfaces best absorbers/emitters of radiation
4Latent heat: energy for change of state, temperature constant

Pakistan Example

Karachi's Summer Heat and Rooftop Water Tanks — Thermodynamics

In Karachi's 40°C summers, exposed black water tanks heat up rapidly (dark surfaces absorb radiation). Installing white-painted or reflective tanks reduces heating. Calculating how much energy KESC/K-Electric uses to pump water to overhead tanks uses Q = mcΔT. AKU Physics papers frequently set heat capacity questions using water and everyday Pakistani contexts.

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