Setting up an online Physics lesson.

 Setting up the Microwave transmitter and receiver, and an oscilloscope for an online lesson. We were experiencing issues with Zoom automatically muting the sound from the receiver, so we needed to find a workaround to ensure the students could hear what was happening.

Exploring Reflection, Refraction, and Diffraction Using Microwaves

When we think of reflection and refraction, most people imagine light bouncing off mirrors or bending through water. But the same phenomena apply to microwaves—a form of electromagnetic radiation with much longer wavelengths than visible light. In this practical blog, we’ll explore how to use a microwave transmitter and receiver alongside metal plates and partially reflective screens to visualise these wave behaviours in the classroom or lab.

Equipment Required

• Microwave transmitter (typically around 10 GHz)

• Microwave receiver (with an output meter)

• Metal reflector plates (aluminium sheets work well)

• Wire mesh or plastic screen (partially reflective material)

• Rotating turntable or protractor stand

• Slits made from two parallel metal plates (for diffraction)

• Dielectric block (e.g., polystyrene for refraction)

• Graph paper or marker board (optional, for plotting)

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Part 1: Reflection of Microwaves

Setup:

Place the microwave transmitter and receiver at the same height, facing each other a short distance apart. Now introduce a metal plate (acting as a mirror) at an angle between the two.

What to Do:

Rotate the metal plate and observe how the intensity at the receiver changes.

What Happens:

Just like light, microwaves follow the law of reflection:
Angle of incidence = Angle of reflection.

You can show this clearly by placing the transmitter and receiver at equal angles to the normal of the metal plate. The receiver signal will peak when this condition is met. This experiment helps confirm that microwaves behave like light in terms of bouncing off reflective surfaces.

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Part 2: Refraction of Microwaves

Setup:

Use a dielectric block such as a rectangular polystyrene prism. Place it in the path between the transmitter and receiver.

What to Do:

Rotate the block and measure the change in the signal strength at different angles of incidence.

What Happens:

Microwaves slow down and change direction when they enter a different medium (just like light entering glass or water). You’ll observe refraction—the bending of waves as they pass from air (low density) into polystyrene (higher density). The amount of bending depends on the refractive index of the block and the wavelength of the microwaves.

This experiment demonstrates that Snell’s Law applies to microwaves:

$$\frac{\sin i}{\sin r} = \frac{v_1}{v_2}$$

where $i$ and $r$ are the angles of incidence and refraction, and $v_1$ and $v_2$ are the wave velocities in each medium.

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Part 3: Diffraction of Microwaves

Setup:

Create a slit using two parallel metal plates, separated by a few centimetres—just about the same size or slightly larger than the microwave wavelength (~3 cm for 10 GHz). Place the transmitter on one side of the slit and scan the receiver across the other side.

What to Do:

Move the receiver left to right in a wide arc, recording the signal intensity at various positions.

What Happens:

You’ll observe a classic diffraction pattern—a central peak with smaller side lobes. The waves bend around the edges of the slit and interfere with each other. This is a strong visualisation of how wave behaviour emerges most clearly when the obstacle or gap is close to the wavelength in size.

Try narrowing the slit. You’ll find the diffraction effect becomes more pronounced—the beam spreads wider. Widen it too far and the wave mostly travels straight through with minimal spreading.

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Bonus: Partially Reflective Screens

You can introduce a fine wire mesh or plastic screen to demonstrate partial transmission and reflection. The signal received will decrease compared to full transmission, and some energy may be reflected back. This opens up discussion about absorption, interference, and how microwave ovens use metal meshes to contain microwaves while letting visible light out.

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Conclusion

These simple but powerful experiments make wave theory tangible. Students can see (or rather, measure) how microwaves reflect off metal, refract through different materials, and diffract around obstacles—just like light and water waves.

They’re also a fantastic reminder that electromagnetic radiation is one big family, differing only in wavelength. By working with microwaves in the lab, you’re not just studying an invisible force—you’re watching the laws of physics unfold, one wave at a time.