Tyndall effect is observed during the projection in a cinema theatre. Why?

Explanation

### Step-by-Step Solution:

1. **Understanding Tyndall Effect**: The Tyndall effect is the scattering of light by colloidal particles. When light passes through a colloid, it gets scattered in different directions due to the presence of these particles.

2. **Brownian Motion**: In a colloidal solution, the particles are in constant random motion, known as Brownian motion. This motion contributes to the scattering of light as the particles collide with the light waves.

3. **Presence of Colloidal Particles in Air**: In a cinema theatre, the air contains tiny dust particles and other colloidal substances, which can be considered as aerosols. These particles are small enough to be suspended in the air and are responsible for scattering light.

...