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๐ฌ Think about it
Hold up clear glass, then tracing paper, then cardboard in front of a torch. The light behaves differently each time. Why do some things let light through and others block it? Let us sort materials by how light passes through them.
How does light pass through different materials?
- Light passes almost completely through transparent materials.
- Light passes partially through translucent materials.
- Light does not pass through opaque materials.
- We can sort materials by how much light passes.
Example:
Clear glass is transparent, tracing paper is translucent, and cardboard is opaque.
Type of material
How light passes
Transparent (glass)
Light passes almost completely
Translucent (tracing paper)
Light passes partially
Opaque (cardboard)
Light does not pass
In this Activity, we will hold different materials in front of a torch and sort them.
Materials needed
Objects made of different materials (cardboard, paper, glass, tracing paper, thick cloth) and a torch.
Procedure
1. List the materials in Table 11.1.
2. In a dark room, make a spot of light from the torch on a wall or screen.
3. Predict whether light will pass if you hold each object in front of the torch.
4. Note your prediction in Table 11.1.
5. Now place each object between the torch and the screen and observe.
6. Repeat this for all the objects.
2. In a dark room, make a spot of light from the torch on a wall or screen.
3. Predict whether light will pass if you hold each object in front of the torch.
4. Note your prediction in Table 11.1.
5. Now place each object between the torch and the screen and observe.
6. Repeat this for all the objects.
Table 11.1 — Light through different materials
| Material | Transparent / Translucent / Opaque | Light will pass fully / partially / not at all | |
|---|---|---|---|
| My prediction | My observation | ||
| Cardboard | Opaque | Not at all | Not at all |
| Paper | Translucent | Partially | Partially |
| Glass | Transparent | Fully | Fully |
| Tracing paper | Translucent | Partially | Partially |
| Thick cloth | Opaque | Not at all | Not at all |
Observation
Light passes fully through glass, partially through paper and tracing paper, and not at all through cardboard and thick cloth.
Explanation
Materials differ in how much light they let through. So they are sorted into transparent, translucent, and opaque.
โ Summary
- Objects held before torch
- Glass let light through
- Cardboard blocked light
- Three material types found
๐งฌ Dive Deeper
- A laser beam is passed through water with a drop of milk added.
- The drop of milk makes the beam easy to see.
- The beam follows a straight path inside the water.
- Use a low-power laser only under a teacher's supervision.
- Light can sometimes bend around corners, learnt in higher grades.
Important Points
- Transparent materials let light pass almost fully.
- Translucent materials let light pass partially.
- Opaque materials block light fully.
โ Test Yourself
-
What is a transparent material?
View Answer
One that lets light pass almost completely, like glass. -
What is a translucent material?
View Answer
One that lets light pass partially, like tracing paper. -
What is an opaque material?
View Answer
One that does not let light pass, like cardboard. -
Why add a drop of milk to water in the laser activity?
View Answer
To make the laser beam easy to see. -
Who should supervise the laser activity?
View Answer
A teacher.
Important Definitions
- Transparent material — a material through which light passes almost completely, like glass.
- Translucent material — a material through which light passes partially, like tracing paper.
- Opaque material — a material through which light does not pass, like cardboard.
