SPM Physics Amali: Refraction & Partial Reflection at Glass-Air Boundary (Amali Optics Real-Lab Demo)

 

I carried out this experiment myself in the Physics laboratory and captured the result as a reference for SPM Physics students.

At first glance, it looks like a simple laser beam passing through a glass block.

Look a little closer.

In a single photograph, you can clearly observe:

✅ Refraction as the laser enters the glass block

✅ Partial Reflection at the glass-air boundary

✅ Refraction Again as the beam exits the glass

That faint upward ray is not a mistake. It is a real reflected ray produced at the boundary, while the rest of the light continues through the glass according to the laws of refraction.

What makes this photo even more special is that the glass block is placed directly on one of my AHA! Crab Optics Posters, turning a textbook diagram into a real laboratory observation.

When Light Travels Along the Normal

In this setup, the incident ray travels parallel to the normal.

This means:

✅ Angle of incidence, i = 0°

✅ Angle of refraction, r = 0°

According to Snell's Law:

When light enters a new medium at 0° incidence, it changes speed but not direction.

The light slows down inside the glass, but because it strikes the surface along the normal, there is no bending.

A Subtle but Important Idea

Although the ray does not bend, something still changes.

✅ Speed decreases inside the glass.

✅ Wavelength decreases.

✅ Frequency remains unchanged.

So even when the path appears unchanged, the Physics is still happening.

AHA! Same glass. Same light. Three different outcomes. Reflection, refraction, or no change in direction at all. Physics is not about memorising rules. It's about knowing when each rule applies.