Polarisation of Light & Microwaves

 One challenge of online tuition is showing experiments clearly—like light polarisation. By positioning a visualiser just right, the effect becomes visible on screen and the learning goal is achieved.

Polarisation of Light and Microwaves: Two Sides of the Same Wave

One of the most fascinating aspects of electromagnetic waves—whether they’re the visible light we see or the microwaves that heat our leftovers—is that they can be polarised. Understanding polarisation not only deepens students’ grasp of wave behaviour but also bridges the gap between different parts of the electromagnetic spectrum. Best of all, it can be demonstrated both in a school lab and during online lessons with the right equipment and camera angles.

What Is Polarisation?

Polarisation refers to the orientation of the oscillations of the electric field in a transverse wave. In unpolarised light, the electric field vibrates in multiple directions. When light (or any electromagnetic wave) is polarised, its electric field oscillates in just one direction.

Polarising Light: A Simple Classroom (or Online) Demo

You will need:

• A light source (a torch or mobile phone torch will do)

• Two polarising filters (Polaroid sheets)

• A white screen or piece of paper

• A visualiser or camera for online teaching

What to do:

1. Shine the light through the first polarising filter. The light is now plane-polarised.

2. Place the second polarising filter (the analyser) in the path of the light.

3. Rotate the analyser. As it turns, you’ll observe the light intensity reduce, eventually reaching zero when the filters are at 90° to each other. This is because the second filter blocks the direction of polarisation imposed by the first.

How to show this online:
Use a visualiser and position it so both filters and the light beam are visible to the webcam. Students can clearly see the light fade and reappear as you rotate the analyser—demonstrating polarisation in action.

Polarising Microwaves: A Bigger Version of the Same Idea

Microwaves are also transverse electromagnetic waves, but they’re much longer in wavelength than visible light. You can demonstrate their polarisation using equipment commonly found in A-Level physics labs.

You will need:

• A microwave transmitter and receiver (often 10 GHz)

• A metal grille (acting as a polariser)

• A rotating mount or protractor

What to do:

1. Align the transmitter and receiver so they’re facing each other with a clear path.

2. Place the metal grille between them. The grille acts like a polarising filter—it absorbs electric field components aligned with the rods.

3. Rotate the grille. As you do, the signal received drops, reaching a minimum when the rods are aligned with the electric field of the wave.

The principle is exactly the same as with light. The only difference is the scale: instead of polarising sheets, we use metal rods spaced about a centimetre apart to block or allow the wave.

What’s the Connection?

Both demonstrations work on the same fundamental principle: the filtering of wave oscillations by alignment. Whether it’s the tiny molecules in a polarising film absorbing certain vibrations of visible light, or metal rods absorbing electric fields in microwaves, the underlying physics is the same.

This provides a powerful teaching point: all electromagnetic waves behave similarly, regardless of frequency or wavelength.

Why It Matters

Teaching polarisation using both light and microwaves:

• Reinforces the nature of transverse waves.

• Highlights the universality of electromagnetic wave behaviour.

• Links abstract theory with hands-on observation.

• Builds skills in experimental design and interpretation.

In online settings, careful camera placement and explanation can bring these concepts to life just as effectively as in a traditional classroom—especially when students see the same principle demonstrated at two different wavelengths.

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Conclusion:
Whether you're bending light with a polarising filter or rotating a microwave grille to block a signal, the takeaway is the same: electromagnetic waves can be filtered by orientation. Polarisation is more than a party trick with sunglasses—it's a window into wave physics that works across the spectrum.