8.0 LIGHT

Light is a form of energy that enables us to see. It travels in straight lines and interacts with materials in various ways. This chapter explores the fundamental nature of light, how it behaves when it meets surfaces (reflection), and how shadows and images are formed. These concepts are the foundation for understanding optics.

8.1 RECTILINEAR PROPAGATION OF LIGHT

Rectilinear propagation means that light travels in straight lines in a uniform medium (same material, same density). This is a basic property of light and is the reason we have sharp shadows.

8.1.1 Experimental Evidence

The three-cardboard experiment:

• Take three cardboard sheets with a small hole at the same height in each. Set them up in a straight line with a candle (or light bulb) behind one end.
• If you look from the far end, you can see the candle flame only when all three holes are aligned in a straight line.
• If you move any of the cards slightly out of line, the light is blocked and you cannot see the flame.
• Conclusion: This shows that light travels in straight lines.

Using straight and bent pipes: If you look through a straight pipe, you can see a light source at the other end. If you bend the pipe, you cannot see the light. This simple demonstration proves light does not go around corners.

8.2 SHADOWS AND ECLIPSES

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