If you place a torch vertically upward, the light ray emitted from the torch will continue to travel until it encounters an object or a medium that either absorbs or scatters the photons. The distance the light ray can travel depends on various factors, such as the power of the torch, atmospheric conditions, and the presence of obstructions.
In a vacuum, where there is no medium to interact with, light can theoretically travel indefinitely. However, in the Earth's atmosphere or any other medium, the light ray will eventually encounter particles or molecules that can absorb or scatter the photons, causing the light to diminish in intensity or completely stop.
When light interacts with matter, such as air molecules, dust particles, or any other obstacle, several things can happen to the photons:
Absorption: The photons can be absorbed by the material they encounter. In this case, the energy of the photons is converted into other forms, such as heat.
Scattering: The photons can be scattered in different directions by the particles they encounter. This scattering can be elastic (without a change in wavelength) or inelastic (with a change in wavelength).
Reflection: If the light ray encounters a reflective surface, such as a mirror or a shiny object, it can bounce off and change direction.
Refraction: When light passes from one medium to another with a different optical density, such as from air to water or from air to glass, it can change direction and speed due to refraction.
The distance the light ray will travel before stopping depends on the specific conditions and the presence of objects or mediums that can interact with the photons. In everyday situations, light can travel significant distances before being absorbed or scattered, allowing us to see objects at varying distances from a light source.