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Materials Around Us - Transparency, Opacity, and Translucency

Grade 6CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Transparency: Materials that allow light to pass through them completely are called transparent materials. We can see through them clearly. Examples include glass, air, and pure water (H2OH_2O).

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Opacity: Materials that do not allow any light to pass through them are called opaque materials. We cannot see through them at all. Examples include wood, cardboard, and metals like Iron (FeFe).

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Translucency: Materials that allow only a portion of light to pass through them are called translucent materials. Objects seen through them appear blurred or hazy. Examples include butter paper, frosted glass, and thin plastic sheets.

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Interaction of Light: When light hits an object, it can be transmitted (pass through), reflected (bounce back), or absorbed. The degree of transparency depends on the ratio of transmitted light to incident light.

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Visibility: For an object to be seen through a material, the light reflected from that object must reach our eyes through the material with minimal scattering.

📐Formulae

Total Incident Light=Transmitted Light+Reflected Light+Absorbed Light\text{Total Incident Light} = \text{Transmitted Light} + \text{Reflected Light} + \text{Absorbed Light}

Transparency (Conceptual)∝Transmitted LightIncident Light\text{Transparency (Conceptual)} \propto \frac{\text{Transmitted Light}}{\text{Incident Light}}

For Opaque Objects: Transmitted Light=0\text{For Opaque Objects: } \text{Transmitted Light} = 0

💡Examples

Problem 1:

A shopkeeper prefers to keep biscuits and sweets in glass or plastic jars rather than wooden boxes. Why?

Solution:

Glass and certain plastics are transparent materials.

Explanation:

Transparent materials allow light to pass through (Itransmitted≈IincidentI_{transmitted} \approx I_{incident}), making it easy for buyers to see the contents clearly without opening the containers.

Problem 2:

While performing an experiment, a student places a sheet of oiled paper in front of a torch. Describe the visibility of the light source.

Solution:

The light source will appear faint and blurred; the paper is translucent.

Explanation:

Oiling the paper fills the gaps between fibers, allowing some light to pass through while scattering the rest. This partial transmission defines translucency.

Problem 3:

Identify the type of material if the percentage of light transmitted is 0%0\%.

Solution:

The material is Opaque.

Explanation:

By definition, if Transmitted Light=0\text{Transmitted Light} = 0, the material does not allow light to pass through, categorizing it as opaque.