WAVE BEHAVIOUR

REFLECTION

Waves reflect, we all know that! Especially light waves, that's how we see. But light waves aren't the only waves that reflect. What about old echoing sound waves? Radio waves? Water waves. On reflection, we may need to look at this again... which is exactly what we did while making this thrilling reflective video.... Join Professor Ryan Fox in his global search for science knowledge.

Light waves are the small part of the electromagnetic spectrum that our human eyes have evolved to detect. This is because light waves reflect so well off most objects. Luminous objects like the Sun (stars) give out visible light and light reflects off other objects like planet, moons, books, trees and other humans really well. Most things are non luminous and need to reflect light so we can see it.

Not every thing reflects light. Transparent objects, like glass, plastic, water and the gases in our atmosphere allow light to pass straight through them. Objects that don't allow light to be transmitted are called opaque. Either the light is reflected by the objects or absorbed. Black objects are very good at absorbing light.

The angle the light hits a surface at is called the angle of incidence. The angle of reflection is always equal to the angle of incidence. This applies to all waves and is called the first law of reflection.

I feel like I am being a little patronising so I shall stop! In the next section - lets look at how sound waves reflect!

SOUND REFLECTING - ECHOES

Echoes are dead useful science geeks. From using sound waves for Sonar, or radio and microwaves for RADAR, or mapping the surface of planets, it is a n essential tool in modern life and research. Let’s look at Sonar first

Sonar stands for Sound Navigation and Ranging. It's a technique that uses sound waves to detect and locate objects underwater. There are two main types of sonar:

1. Active Sonar: This system emits sound pulses and listens for the echoes that bounce back from objects. It's like underwater echolocation.

2. Passive Sonar: This system listens for sounds made by objects, such as submarines or marine life, without emitting any sound

Sonar is widely used in various fields, including:

- Military: For detecting submarines and underwater mines.

- Navigation: Helping ships and submarines navigate safely.

- Research: Mapping the ocean floor and studying marine life

Sonar technology has played a significant role in the search for the Loch Ness Monster, often referred to as "Nessie." Here, using cutting edge animation (at least for the time it was filmed in 2003, we see how sonar can be applied and the theory applied. Join us, as a younger version of our chief science geek, armed with an old fashion video camera, embarks on a quest to find the elusive creature. Emotional, moving stuff…. Warning… also contains “Biology”.

Bats use ultrasonic waves and echo location to hunt pray.... as do dolphins! In this rejected pixar movie.... a talking bat explains how it works. Honest.

And let's not forget! Ultrasound, high frequency sound waves, are used during pre-natal scans so that we can see how cute little babies are developing in the womb! The sound waves are harmless to the baby and it works because the ultrasound waves are partially transmitted and partial reflected as they pass through the different types of tissues of both the mother and the baby. These amazing machines process the reflected sound waves and form complex images of the baby and it's internal organs. Sometimes science is just too amazing.....

Refraction

Light changes direction as it moves from one substance to the other. Who cares? You should, it's why lenses work and allow us to make things from spectacles and projectors to contact lenses and telescope lenses. But once again, it's not only light that refracts. Other waves do too. Water waves on a beach. Sound waves through walls. Seismic waves through the complex interior of our entire planet. But more on those later. First let us understand how light is refracted with this worryingly, disturbed puppet video. No puppets were harmed in the making of this video, only children. It was the 90's back then. Things were more relaxed.

So why do waves refract? Will in the case of light, it's because the light waves travel slower in optically denser transparent materials. When the light hits the denser material at an angle part of the wave front slows down first causing the light to change direction. As it leave the denser medium and enters a less dense medium it speeds up again!

The refraction of light and why it happens can be investigated further in this wonderful "interactive wotsit" from our friends at Phet!

Here are some possible things for you to try:

• Explain how light bends at the interface between two media and what determines the angle.

• Apply Snell’s law to a laser beam incident on the interface between media.

• Describe how the speed and wavelength of light changes in different media.

• Describe the effect of changing wavelength on the angle of refraction.

• Explain how a prism creates a rainbow.

TOTAL INTERNAL REFLECTION

Total Internal Reflection, or TIR for short, is one of the most important bits of Physics ever! And I mean ever! What's that? You really don't care! Well you should..... its the internet! It's broadband! It's how optical fibres work. With out it there would be no streaming, no social media sharing of selfies and videos, nothing of use on the internet at all! The world of the modern youth would not exist! So what is it and how does it work. Here we have another appalling video to explain it. Enjoy!

DIFFRACTION

GCSE students, watch this for fun! Everybody watch it for fun! Diffraction! Science comedy horror animated education - an often overlooked genre.... ! But diffraction is essential concept in physics! It affects our communications, proved that electrons behave like waves sometimes, enabled us to work out the composition of different stars by studying their light and lead to the development of electron microscopes. Meanwhile.....join us in the classic physics adventure in "THE VALLEY OF THE DAMNED!"