krit.club logo

Light and Sound - Reflective materials

Grade 3IGCSE

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

🔑Concepts

•

Light travels in straight lines. This can be represented as a ray: LrayL_{ray}.

•

Reflection occurs when light hits a surface and 'bounces' off it. We see objects because light reflects from them into our eyes (Object→EyeObject \rightarrow Eye).

•

Reflective materials are usually shiny, smooth, and flat (like a mirror or polished metal).

•

Non-reflective or dull materials (like wood, carpet, or dark fabric) absorb more light than they reflect.

•

The Law of Reflection states that the angle at which light hits a surface is the same as the angle at which it leaves: θi=θr\theta_{i} = \theta_{r}.

•

Safety clothing uses 'retro-reflective' materials to bounce light back to a source (like car headlights) to keep people visible at night.

📐Formulae

θi=θr\theta_{i} = \theta_{r}

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

💡Examples

Problem 1:

Which material would be the best for a cyclist to wear at night to stay safe: a black cotton t-shirt or a silver metallic vest?

Solution:

The silver metallic vest.

Explanation:

Shiny and light-colored materials reflect more light (LreflectedL_{reflected}) back to the driver's eyes, whereas dark cotton absorbs most of the light, making the cyclist hard to see.

Problem 2:

If a beam of light hits a flat mirror at an angle of 45∘45^\circ from the normal line, what is the angle of reflection?

Solution:

The angle of reflection is 45∘45^\circ.

Explanation:

Based on the formula θi=θr\theta_{i} = \theta_{r}, the angle of incidence and reflection must be equal.

Problem 3:

Why is it harder to see your reflection in a piece of crumpled aluminum foil than in a flat piece of foil?

Solution:

Because the surface is no longer smooth.

Explanation:

On a rough surface, light rays are reflected in many different directions. This is called 'diffuse reflection'. A flat surface allows for 'specular reflection' where rays stay organized, forming a clear image.