2.1 Surface Properties and Heat Transfer

Last updated at May 3, 2026 by

What is Surface Properties and Heat Transfer?

It is the way different surfaces absorb and radiate heat differently based on their colour and texture .

Key Facts and Examples
  • Dark surfaces are better absorbers of heat radiation .
IMG004

A black car seat in sunlight absorbs heat, showing
how dark surfaces get hotter.

Example: Black car seats become very hot in sunlight
  • Light-coloured surfaces reflect heat and stay cooler .
IMG012

A black car seat absorbs heat from the sun, becoming
hot to the touch, illustrating surface heat
absorption.

Example: White clothes keep us cool in summer heat
  • Rough surfaces absorb more heat than smooth surfaces .
IMG020

A person touches a black car seat heated by
sunlight, showing how dark surfaces absorb more
heat.

Example: Rough black cooking pot bottom heats food faster
  • Shiny surfaces reflect radiation and radiate less heat .
Example: Shiny thermos flask keeps drinks hot longer
  • Black surfaces also radiate heat better than light surfaces .
Example: Black-painted radiators cool rooms more efficiently
Dark vs Light Surfaces Property Dark Surfaces Light Surfaces Heat Absorption Absorb more heat Absorb less heat Heat Radiation Radiate more heat Radiate less heat Temperature Get hotter quickly Stay cooler Examples Black clothes, car seats White clothes, walls

Activity 2.1: Comparing Heat Absorption by Different Surfaces (Page 5)

What you need:

  • Two identical metal cans
  • Black paint
  • Cold water (equal amounts)
  • Heat lamp
  • Thermometer

What to do:

  • Step 1: Paint one metal can completely black
  • Step 2: Leave the other can shiny and metallic
  • Step 3: Fill both cans with equal amounts of cold water
  • Step 4: Place them at equal distances from a heat lamp
  • Step 5: Heat for 30 minutes
  • Step 6: Measure the temperature of water in each can

Observations

What you see:

Can Type Initial Temperature Final Temperature Temperature Rise
Black can 25°C 45°C 20°C
Shiny can 25°C 35°C 10°C
  • Black can shows higher temperature after heating
  • Shiny can shows lower temperature after heating
  • Black surface absorbs more radiation from heat lamp
  • Shiny surface reflects more radiation away
Why this happens:

We have studied that dark surfaces are better absorbers of heat radiation . This is why the black can heated up more than the shiny can .

  • Dark colours absorb most wavelengths of light energy
  • Light colours reflect most wavelengths of light energy
Heat Absorption Process Heat lamp radiates Energy travels as radiation Black surface absorbs Most energy absorbed Shiny surface reflects Most energy bounced back Black can gets hotter!

Section Summary: Effects of Colour and Nature of Surface on Radiation

Surface Properties Summary Dark Surfaces Better heat absorbers and radiators Light Surfaces Poor absorbers, good reflectors Practical Uses Clothing, cooking, insulation
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