AQA GCSE Physics: Waves Revision Notes

Wave Basics and Types

Ever wondered how your voice reaches someone across the room? Waves transfer energy from one place to another whilst the particles that make up the wave simply oscillate about a fixed point. Think of it like a Mexican wave at a football match - the energy moves around the stadium, but each person stays in their seat.

There are two main types of waves you need to know. Transverse waves have oscillations perpendicular to the direction of energy transfer - imagine ripples spreading across a pond when you drop a stone. The water doesn't actually travel outwards with the ripples.

Longitudinal waves have oscillations parallel to the direction of energy transfer, like sound waves travelling through air. These waves have key properties: frequency (waves passing a point each second), amplitude (maximum displacement), wavelength (distance between equivalent points), and period (time for one complete oscillation).

Quick Tip: Remember the wave equation: wave speed = frequency × wavelength. This applies to all waves and is essential for calculations!

Wave Behaviour: Reflection, Refraction, and Diffraction

When waves hit boundaries between different materials, fascinating things happen. Reflection occurs when waves bounce back - think of looking in a mirror. The angle of incidence always equals the angle of reflection, measured from the normal (perpendicular line).

Refraction is when waves change direction as they enter a new medium. This happens because the wave speed changes whilst frequency stays constant. Light entering glass slows down and bends towards the normal, whilst light leaving glass speeds up and bends away from the normal.

Diffraction is the spreading out of waves, particularly noticeable when waves pass through gaps or around obstacles. The amount of diffraction depends on the wavelength compared to the gap size.

Remember: When waves change medium, frequency never changes, but speed and wavelength do - they're directly proportional!

Sound Waves and Ultrasound Applications

Sound waves make your world vibrant and noisy! These longitudinal waves travel through solids, liquids, and gases by causing particles to vibrate. Inside your ear, sound waves make your eardrum vibrate, creating the sensation of hearing.

Human hearing has limits - we can only detect frequencies between 20 Hz and 20 kHz. The amplitude determines loudness, whilst frequency determines pitch. Higher frequency means higher pitch, which is why a piccolo sounds different from a tuba.

Ultrasound waves have frequencies above 20 kHz and are incredibly useful. They partially reflect at boundaries between different media, allowing doctors to see inside your body safely. Echo sounding uses this principle - ultrasound pulses bounce back from objects, and the time delay tells us the distance using: distance = speed × time.

Fascinating Fact: Ultrasound is used in both medical imaging (seeing unborn babies) and industrial applications (detecting flaws in metal)!

Seismic Waves and the Electromagnetic Spectrum

Earthquakes produce seismic waves that reveal Earth's hidden structure. P-waves (primary) are longitudinal, faster, and can travel through both solids and liquids. S-waves (secondary) are transverse, slower, and crucially cannot travel through liquids - this proves Earth's outer core is liquid!

The electromagnetic spectrum is a family of transverse waves that all travel at the same speed through space. From longest to shortest wavelength: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

Your eyes only detect visible light - a tiny portion of this vast spectrum. Yet each type has unique properties: radio waves carry your favourite stations, microwaves heat your food, and infrared radiation keeps you warm.

Key Point: All electromagnetic waves travel at 300,000,000 m/s in a vacuum - the speed of light!

Electromagnetic Wave Applications and Hazards

Each part of the electromagnetic spectrum has specific uses that affect your daily life. Radio waves transmit television and radio signals safely. Microwaves cook food by making water molecules vibrate, whilst infrared radiation from electrical heaters keeps you warm.

Visible light travels down optical fibres for internet communication. Ultraviolet light sterilises bacteria and creates energy-efficient lighting. X-rays penetrate soft tissue but not bone, making them perfect for medical imaging.

However, some electromagnetic waves are dangerous. Ultraviolet, X-rays, and gamma rays can damage human tissue. UV causes premature skin aging and increases skin cancer risk. X-rays and gamma rays are ionising radiation that can mutate genes and cause cancer.

Radiation dose is measured in sieverts (Sv), with 1000 millisieverts equalling 1 sievert. This measures your risk of harm from radiation exposure.

Safety First: Always protect yourself from excessive UV exposure - use sunscreen and avoid prolonged sun exposure!

Lenses and Image Formation

Lenses form images by refracting light in predictable ways. A convex lens brings parallel light rays together at the principal focus - the distance from lens to focus is the focal length.

Convex lenses can produce both real images (that can be projected on a screen) and virtual images (that cannot). Concave lenses always produce virtual images that appear smaller than the original object.

Magnification tells you how much bigger or smaller an image appears compared to the original object. Calculate it using: magnification = image height ÷ object height. Remember, magnification is a ratio with no units!

Practical Tip: When measuring image and object heights for magnification calculations, use the same units (both mm or both cm) to avoid errors!