Question

The smoke from a fire looks white. Which of the following statements is true?
  1. Molecules of the smoke are bigger than the wavelength of light.
  2. Molecules of the smoke are smaller than the wavelength of light.

Answer 1

Hint: Smoke is a mixture of particles and chemicals which is produced by incomplete burning of carbon containing materials during fire. Smoke is a good example of the process of the scattering of light.

Complete step by step answer:
First of all we see some information about smoke.
1.White smoke can mean that fire is just starting to consume material.
2.It can also indicate the light and flashy fuels such as grass or twigs.
From above two statements, statement 1 is true because molecules of the smoke are bigger than the wavelength of light. This happens because it scatters light from white light of all wavelengths to the same extent, through the process of scattering i.e. light energy is absorbed and reemitted. Due to this reason, smoke from a fire looks white.
So statement 1- ‘Molecules of the smoke are bigger than the wavelength of light’ is true and statement 2 is false.
Additional information:
Different colours of smoke from fire indicate a sign of a burning stage.
Examples: Blue colour of smoke indicates a temperature even hotter than white colour. It appears usually at temperatures between 26000F and 30000F.

Note: Students can remember this concept by understanding the phenomenon of scattering of light. Remember that if the wavelength of light is larger than molecules then scattering of light does not happen.