Question

Name and explain the phenomenon of light due to which the path of a beam of light becomes visible when it enters a smoke filled room through a small hole. Also state the dependence of colour of the light we receive on the size of the particle of the medium through which the beam of light passes.

Answer 1

Step 1: Phenomenon of Light in a Smoke-Filled Room:
The phenomenon that makes the path of a beam of light visible when it enters a smoke-filled room through a small hole is called scattering of light. In this case, the particles of smoke in the air scatter the light in different directions. As a result, we can see the light path because the scattered light reaches our eyes.
- The scattering occurs when the light interacts with small particles in the medium (in this case, smoke). These particles cause the light to deviate from its original path and scatter in different directions, making the beam visible.

Step 2: Dependence of Colour of Light on Particle Size:
The colour of light we see depends on the size of the particles in the medium through which the beam of light passes, according to Rayleigh scattering.
- When the particles are much smaller than the wavelength of light, shorter wavelengths (blue and violet light) scatter more effectively than longer wavelengths (red light). This is why the sky appears blue and the sun appears yellow or red depending on the scattering effect.
- As the particle size increases (e.g., dust or smoke particles), the scattering effect is less dependent on the wavelength. Larger particles tend to scatter all wavelengths of light equally, and the light might appear whitish or hazy.

Step 3: Conclusion:
The path of light becomes visible in a smoke-filled room due to the scattering of light by the smoke particles. The colour of the scattered light depends on the size of the particles in the medium, with smaller particles causing more scattering of shorter wavelengths (blue and violet), while larger particles scatter light more equally, often resulting in a whitish appearance.