The Tyndall effect

The idea

When a beam of light strikes fine particles, such as those in the atmosphere, its path becomes visible because the particles scatter the light; this scattering by colloidal particles gives the Tyndall effect.

A beam in a dusty room

A thin beam of sunlight comes in through a small hole into a room full of smoke. You can see the beam clearly.

Why can you see the path of the beam?

• The smoke particles scatter the light to your eyes
• The light itself glows in the dark
• The smoke makes the light brighter

Beams in different mixtures

Open the tabs.

Scattering

A beam of light is not visible in a true solution, where the particles are very small. It is visible in a colloidal solution, because the particles scatter the light. The earth's atmosphere is a mixture of smoke, tiny water droplets, dust and air molecules, so it scatters light. This scattering by colloidal particles is the Tyndall effect.

When a beam of light strikes fine particles such as those in the atmosphere, its path becomes visible: the particles scatter the light. Scattering by colloidal particles gives the Tyndall effect.

Notes

Fine particles in the atmosphere scatter a light beam, so its path becomes visible: the Tyndall effect, scattering by colloidal particles.

Check yourself

In which solution is the path of a light beam not visible?

The phenomenon of scattering of light by colloidal particles is called…

Which of these is part of the atmosphere?

Where is the Tyndall effect seen, according to the book?

• A colloidal solution. The path of a beam of light becomes visible through a colloidal solution, where the size of the particles is relatively larger.
• A true solution — correct. Yes!
• Both of them. The path is visible through a colloidal solution.
• dispersion. Dispersion is the splitting of light into its colours.
• atmospheric refraction. Atmospheric refraction is the refraction of light by the earth's atmosphere.
• the Tyndall effect — correct. Yes!
• Smoke, tiny water droplets, dust and air molecules — correct. Yes!
• Only air molecules and nothing else. The atmosphere is a heterogeneous mixture of minute particles, including smoke, tiny water droplets, suspended particles of dust and molecules of air.
• Only glass prisms. The atmosphere includes smoke, tiny water droplets, dust particles and molecules of air.
• When light goes through a clear glass slab. The Tyndall effect is seen when a fine beam of sunlight enters a smoke-filled room through a small hole, or when sunlight passes through a canopy of a dense forest.
• When sunlight enters a smoke-filled room through a small hole, or passes through a dense forest canopy — correct. Yes!
• Only at night. It is seen when a fine beam of sunlight enters a smoke-filled room, or through a canopy of a dense forest.