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medium difficulty5 min

Tyndall Effect

The Tyndall effect is the scattering of a beam of light by colloidal particles, making the path of light visible.

In one line: Tyndall tells: tiny colloid particles turn the light path visible.

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Understand it

Colloidal particles are large enough to scatter light, so a light beam passing through a colloid can be seen from the side. True solutions usually do not show this effect because their particles are too small to scatter light noticeably.

Example

A beam of light becomes visible in fog or in a dusty room because tiny particles scatter light.

Rule to remember

Rule: visible light path through a mixture suggests colloidal particles scattering light.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

  1. 1Pass a narrow torch beam through salt solution and diluted milk.
  2. 2The beam path is not visible in salt solution but becomes visible in diluted milk, showing Tyndall effect in the colloid.

Method you can reuse

  1. 1Pass a narrow beam through the sample.
  2. 2Observe from the side.
  3. 3If the path is visible, infer scattering by colloidal particles.
  4. 4If not, it may be a true solution.

Sketch it in your answer

Draw two beakers with a torch beam: path invisible in salt solution and visible in colloid such as milk diluted with water.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why does a colloid show the Tyndall effect but a true solution usually does not?

Think first, then show answer
A colloid shows the Tyndall effect because its particles are large enough to scatter light, while true solution particles are too small to make the light path visible.

Common wrong answer

Saying a visible light path proves a suspension only.

Why it loses marks: Colloids also scatter light clearly.

Don't mix this up

Students sometimes write that any transparent mixture shows Tyndall effect. A true salt solution is transparent but does not show a visible light path.

Exam tip

When answering, mention both cause and use: scattering by colloidal particles helps distinguish colloids from true solutions.

Tyndall Effect diagram

Open full screen to read every label clearly.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Questions ask students to identify the mixture type from a visible light path or explain fog headlights using scattering.
  1. 1

    Enough for 1 mark

    The Tyndall effect is the scattering of a beam of light by colloidal particles, making the path of light visible.

  2. 2

    Add for 2 marks

    Example: A beam of light becomes visible in fog or in a dusty room because tiny particles scatter light.

  3. 3

    Add for 3 marks

    Colloidal particles are large enough to scatter light, so a light beam passing through a colloid can be seen from the side.

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