Chapter 14.1, Problem 4SSC

Interpretation Introduction

Interpretation:

It is more difficult to drive through fog using high beams than using low beams. It can be explained by using Tyndall effect or light scattering effect of colloidal particles.

Concept introduction:

Colloid: A colloid is a two-phasic heterogeneous mixture where one phase is dispersed in another phase, the particle size of the dispersed phase is in between 1 nm to 100 nm. By changing the nature of dispersed phase and dispersion medium, various number of colloids were reported. Fog is an example of aerosol colloid where dispersed phase is liquid and dispersion medium is gas.

Tyndall effect: The Tyndall effect is light scattering propertiesof dispersed particles in a colloid and sometimes this effect is also observed in a very fine suspension. The Tyndall effect was first described by 19th-century physicist John Tyndall. That’s why this effect named after John Tyndall. Tyndall effect can also be observed when afine beam of light enters a room through a smallhole. This happens due to the scattering of lightby the particles of dust and smoke in the air.

Answer to Problem 4SSC

High beams are aimed farther down the road than low beams. Because the fog scatters light, there is less light from the high beams to illuminate the road than from the low beams. Also, because the high beams are aimed more directly towards the fog, more light is scattered back towards the eye, making it more difficult to see.

Explanation of Solution

Fog is a colloid where dispersed phase is liquid and dispersion medium is gas. As a colloid, fog also exhibited Tyndall effect. When a beam of light falls on this colloidal medium (fog), it scatters light. Driving through fog is easier using low beam light. High beams are aimed farther down the road than low beams. Because the fog scatters light, there is less light from the high beams to illuminate the road than from the low beams. Also, because the high beams are aimed more directly towards the fog, more light is scattered back towards the eye, making it more difficult to see.

Conclusion

Due to scattering of light by colloidal particles, it is more difficult to drive through fog using high beams than using low beams.