Wave Basics and Properties

Think of waves as energy messengers - they carry energy from one place to another without actually moving any matter. When you drop a stone in water, the ripples spread outward, but the water itself doesn't travel with them.

Every wave has key measurements you need to know. Amplitude is how far the wave moves from its resting position - bigger amplitude means more energy. Wavelength is the distance of one complete wave cycle, whilst frequency tells you how many waves pass by each second.

The essential formulas are straightforward: f = 1/T (frequency equals one divided by time period) and v = f × λ (wave speed equals frequency times wavelength). For example, if a wave takes 0.5 seconds for one complete cycle, its frequency is 2 Hz.

There are two main wave types: transverse waves (like light and water ripples) oscillate up and down whilst moving forward, and longitudinal waves (like sound) squeeze and stretch in the same direction they're travelling.

Quick Tip: Remember that in wave calculations, always convert centimetres to metres before plugging numbers into formulas!

Reflection - When Waves Bounce Back

When waves hit a boundary between different materials, three things can happen: they might be absorbed (energy gets soaked up), transmitted (they pass through), or reflected (they bounce back). Understanding reflection helps explain how mirrors and echoes work.

Ray diagrams show us the rule: the angle of incidence always equals the angle of reflection. Both angles are measured from an imaginary line called the normal, which sits perpendicular to the surface at 90 degrees.

The type of surface determines what kind of reflection you get. Smooth surfaces like mirrors create specular reflection - all the light bounces off in the same direction, giving you a clear image. Rough surfaces like paper create diffuse reflection - light scatters in all directions, which is why you can't see yourself in a piece of paper.

This explains why you can read this page right now - the paper is scattering light from various sources into your eyes, making the text visible.

Remember: The normal line is always perpendicular to the surface, not necessarily vertical!

Refraction - When Waves Change Direction

Refraction happens when waves change speed as they move from one material to another. Different materials have different densities, and electromagnetic waves like light slow down in denser materials.

Here's the key rule: when light travels from a less dense to a more dense material (like air to glass), it bends towards the normal. When it goes the other way (glass to air), it bends away from the normal. If waves hit the boundary straight on (perpendicular), they just carry on without bending.

Using the wave equation v = f × λ, when speed changes, wavelength must change too because frequency stays constant. If wave speed increases, wavelength increases proportionally.

White light through a prism creates a rainbow because different colours (wavelengths) refract by different amounts. This separation of colours is called dispersion and shows us that white light contains all colours mixed together.

Key Point: Frequency never changes during refraction - only speed and wavelength change!

The Electromagnetic Spectrum

All electromagnetic waves are transverse waves that travel at the same speed in a vacuum: 3 × 10⁸ m/s (the speed of light). They only slow down and refract when passing through different materials.

The electromagnetic spectrum arranges these waves by wavelength and frequency. From longest wavelength to shortest: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Wavelength and frequency are inversely related - as one increases, the other decreases.

Humans can only detect visible light, which is a tiny portion of the spectrum. Within visible light, we see colours from red (longest wavelength) to violet (shortest wavelength) - remember ROYGBIV.

Different electromagnetic waves come from various sources: gamma rays from radioactive decay, visible light and UV from electrons changing energy levels, and infrared from vibrating molecular bonds. All electromagnetic waves can be absorbed, reflected, or transmitted.

Memory Trick: "Radio Microwave Infrared Visible Ultraviolet X-ray Gamma" - the spectrum from lowest to highest energy!

Radio Waves and Communication

Radio waves have the longest wavelengths and lowest frequencies in the electromagnetic spectrum. We generate them using alternating current - basically oscillating electric charges in a transmitter connected to an aerial.

The transmission process is clever: a transmitter creates radio waves at a specific frequency, which travel through space and get picked up by a receiver. The receiver converts the radio wave back into an alternating current with the same frequency, allowing information transfer.

Different radio wave frequencies work best for different purposes. Long waves can diffract (bend) around Earth's curved surface, making them perfect for long-distance communication. Short waves can't curve around Earth, but they bounce off the ionosphere (a charged layer in the upper atmosphere), allowing them to travel huge distances by bouncing back and forth.

Very short radio waves (used for TV and FM radio) travel in straight lines from transmitter to receiver, which is why hills and tunnels can block your signal.

Fun Fact: Bluetooth uses very short radio waves, which is why it only works over short distances!

Microwaves and Infrared Radiation

Microwaves work brilliantly for heating food because they're absorbed specifically by water molecules. In a microwave oven, these waves make water molecules vibrate faster, and this energy spreads through food via conduction and convection.

For satellite communication, we use microwaves that aren't absorbed by atmospheric water. These waves pass through the atmosphere, get received by satellites, then bounce back to Earth where satellite dishes detect them.

Infrared radiation is emitted by all objects with thermal energy - the hotter something is, the more infrared it gives off. This is why infrared cameras can spot living organisms in the dark and why you feel heat from a fire even before touching it.

Common infrared applications include cooking (ovens and grills heat metal that emits infrared to cook food surfaces) and electric heaters (which warm rooms by emitting infrared radiation). Unlike microwaves, infrared doesn't penetrate deeply - it mainly heats surfaces.

Both microwaves and infrared are generally safe in normal quantities, though high concentrations can cause burns.

Safety Note: Background microwave and infrared radiation is harmless - it's only dangerous in concentrated amounts!

High-Energy Waves and Their Uses

UV light, X-rays, and gamma rays are the high-energy end of the electromagnetic spectrum and can be seriously hazardous. Radiation dose measures how much exposure causes harm to humans.

UV radiation ages skin prematurely and increases skin cancer risk - that's why sun cream is essential. X-rays and gamma rays are ionising radiation that can mutate genes and cause cancer, so exposure should be minimised with protective equipment.

Despite the dangers, these high-energy waves have brilliant practical uses. Radio waves work perfectly for TV and radio because their long wavelengths travel far without losing quality. Microwaves penetrate the atmosphere for satellite communication and cook food efficiently.

Infrared transfers thermal energy for cooking and thermal imaging. Visible light works best for fibre optics because it reflects well in glass fibres. UV light is used for sun tanning and energy-efficient lamps. X-rays (and gamma rays) have enough energy to penetrate materials for medical imaging and cancer treatment.

Each wave type's properties make it perfect for specific jobs - it's all about matching the right wave to the right application.

Key Insight: Higher energy electromagnetic waves are more dangerous but also more useful for penetrating materials!