Understanding Physics: Waves and Radiation Fundamentals

Introduction to Waves

Think of waves as nature's delivery service - they transfer energy from one place to another without moving any actual material. Whether it's the bass from your speakers or light from your phone screen, waves are constantly moving energy around you.

Wave basics are pretty straightforward once you get them. Frequency is how many waves pass a point every second (measured in hertz), whilst wavelength is the distance between two wave peaks. Amplitude determines how much energy the wave carries - bigger amplitude means more energy.

There are two main types: transverse waves (like light, where particles vibrate perpendicular to the wave direction) and longitudinal waves (like sound, where particles vibrate parallel to the wave direction). The key relationship you'll use loads is: wave speed = frequency × wavelength.

Quick Check: Remember that period and frequency are opposites - if frequency doubles, period halves!

Sound Waves and Audio

Sound waves are longitudinal waves that need a medium to travel through - they'll zip through solids, liquids, and gases, but they can't cross a vacuum (which is why space films get it wrong with those epic explosion sounds!).

Pitch and volume are dead easy to understand. Higher pitch means higher frequency - a squeaky voice has more waves per second than a deep voice. Louder sounds have greater amplitude, which you can spot on oscilloscope traces as taller waves.

Human hearing ranges from 20 Hz to 20,000 Hz, but ultrasound (frequencies above 20,000 Hz) has brilliant uses in medicine for scans and in industry for cleaning. Sound levels are measured in decibels, and excessive noise can damage your hearing - that's why ear protectors are essential in noisy environments.

Musical instruments work by controlling frequency: shorter guitar strings or tighter strings produce higher pitches, just like shorter air columns in wind instruments.

Real World: Thunder and lightning show that light travels much faster than sound - you see the flash before hearing the boom!

More Wave Properties

Diffraction is when waves bend around obstacles or spread through gaps - it's why you can hear someone calling from around a corner even when you can't see them. The amount of diffraction depends on wavelength compared to the obstacle size.

Amplifiers are crucial for sound systems. A microphone converts sound to electrical signals, the amplifier boosts these signals (keeping the same frequency but increasing amplitude), and the loudspeaker converts them back to sound waves.

Your recorded voice sounds different to you because normally you hear your voice through bone conduction as well as air, but recordings only capture the air-transmitted sound. This is why most people don't like hearing their recorded voice!

Measuring sound speed in air is straightforward using distance, time and speed calculations - you'll often use values around 340 m/s for sound in air.

Physics Tip: Wave calculations using speed = frequency × wavelength work for all waves - sound, light, radio waves, the lot!

Electromagnetic Spectrum

The electromagnetic spectrum is like a massive family of waves, all travelling at the speed of light but with different wavelengths and frequencies. From highest to lowest wavelength: gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, TV and radio waves.

Here's the crucial bit: higher frequency means more energy. Gamma rays pack serious energy and can be dangerous, whilst radio waves are low energy and safe. Each type has different sources and detectors - your mobile phone detects microwaves, your eyes detect visible light, and X-ray machines both produce and detect X-rays.

Applications are everywhere in daily life. Radio waves carry your music and phone signals, microwaves heat your food and enable WiFi, infrared lets you use TV remote controls, UV light helps your body make vitamin D (but too much causes sunburn), X-rays show broken bones, and gamma rays can treat cancer.

The electromagnetic spectrum explains how we can have wireless technology, medical imaging, and even why the sun gives us both light and warmth.

Remember: All electromagnetic radiation travels at 300,000,000 m/s in a vacuum - that's the speed of light!

Light Behaviour

Refraction happens when light changes speed moving between materials, causing it to change direction. Light bends towards the normal (perpendicular line) when entering glass from air, and away from the normal when leaving glass. This bending creates the angles of incidence and refraction.

Lenses are shaped glass that control light paths. Converging lenses (thicker in the middle) bring parallel rays together and correct long sight, whilst diverging lenses (thinner in the middle) spread rays apart and correct short sight.

Total internal reflection occurs when light hits a boundary at more than the critical angle - instead of passing through, it reflects completely. This principle makes optical fibres work, allowing light signals to travel long distances through glass cables for internet and communications.

Light also follows the law of reflection from mirrors: angle of incidence equals angle of reflection, both measured from the normal. These principles explain everything from why glasses work to how fibre optic broadband reaches your home.

Practical Tip: Remember that light always takes the quickest path, which isn't always the shortest due to different speeds in different materials!

Nuclear Radiation Basics

Atoms consist of a nucleus (containing protons and neutrons) surrounded by electrons. Some atoms are unstable and emit nuclear radiation to become more stable, releasing energy that can be absorbed by surrounding materials.

The three main types are alpha particles (2 protons + 2 neutrons), beta particles (high-speed electrons), and gamma rays (electromagnetic radiation). Alpha particles travel only a few centimetres in air and are stopped by paper, beta particles travel further and need aluminium to stop them, whilst gamma rays are very penetrating and require lead shielding.

Ionisation occurs when radiation knocks electrons off atoms, creating charged particles. Alpha particles create much denser ionisation than beta or gamma radiation, making them more dangerous inside the body but easier to shield against.

Background radiation comes from natural sources (cosmic rays, rocks, radon gas) and artificial sources (nuclear weapons testing, medical procedures, nuclear accidents). Everyone receives some background radiation - it's completely normal and usually harmless at low levels.

Safety First: The three key principles for radiation protection are time, distance, and shielding - limit exposure time, maximise distance, and use appropriate barriers.

Radiation Dosimetry

Absorbed dose (D) measures the energy absorbed per kilogram of material, measured in grays (Gy) where 1 Gy = 1 joule per kilogram. You'll calculate this using D = E/m (energy divided by mass).

However, biological damage depends on more than just absorbed dose. Different radiation types cause different amounts of biological harm, so each gets a radiation weighting factor (wR). Alpha radiation is much more dangerous than gamma radiation for the same absorbed dose.

Equivalent dose (H) combines absorbed dose with radiation type: H = D × wR, measured in sieverts (Sv). This gives a better picture of actual biological risk. Equivalent dose rate shows how quickly you're receiving dose over time.

These measurements help medical professionals and radiation workers stay safe. A chest X-ray gives about 0.1 mSv, whilst the annual limit for radiation workers is 20 mSv. Understanding these units helps you put radiation risks in perspective.

Key Formula: Remember the progression - energy absorbed becomes absorbed dose, which becomes equivalent dose when you account for radiation type.

Activity and Half-life

Activity measures how many radioactive atoms decay each second, measured in becquerels (Bq) where 1 Bq = 1 decay per second. You can calculate activity using A = N/t (number of decays divided by time).

Half-life is the time taken for half the radioactive atoms to decay, or for activity to halve. It's like a radioactive countdown that never quite reaches zero - after one half-life you've got 50% left, after two half-lives 25%, after three half-lives 12.5%, and so on.

Safety procedures with radioactive materials include wearing gloves and lab coats, using tongs to handle sources, storing materials in lead-lined containers, and displaying radioactive hazard signs. The ALARA principle (As Low As Reasonably Achievable) guides all radiation work.

You can reduce equivalent dose through three methods: shielding (barriers between you and the source), time (minimising exposure duration), and distance (radiation intensity decreases with distance squared).

Memory Trick: Half-life is like a countdown that halves each step - 100%, 50%, 25%, 12.5%, 6.25%...