An unlit incense stick(agarbatti) gives smell only when we come close to it but onlighting the stick we get smell even far away from it, why ?
The particles of a solid have large forces of attraction between their molecules and cannot move freely. Diffusion of fragrance is very less because of which the smell is not reached to a far distance. On heating/ lighting the incense stick vapourises i.e. converts into the gaseous phase, and so the attraction becomes less and particles are free to move. as the particles of matter are in continous motion, the particles of the incense stick move continuosly, diffuse faster and reach a farther distance.