Physics: Waves and Radiation

Ionising Radiation

• X-rays and Gamma rays are types of ionising radiation that can lead to mutations and cancer.
• Minimizing exposure is crucial; protective shielding should use dense materials like lead.

Light and Sound Waves

• Light waves are transverse, characterized by peaks and troughs, and they vibrate at right angles to their direction of travel.
• Sound waves are longitudinal, featuring compressions and rarefactions, with vibrations in the direction of travel.

Reflection and Refraction

• Reflection occurs when light bounces off a surface, such as a plane mirror, and can be illustrated through ray diagrams.
• Refraction happens when light passes through different media, altering its angle; denser media slow down light leading to bending towards the normal.
• Snell's law: n1 * sin(i) = n2 * sin(r), where n represents refractive index, i is the angle of incidence, and r is the angle of refraction.

Total Internal Reflection

• Occurs at the critical angle; when light hits a boundary at an angle greater than the critical angle, it reflects back into the denser medium, common from glass to air.
• The critical angle is defined by n = 1/sin(c) where n is the refractive index and c is the critical angle.

Optical Fibres

• Composed of glass with cladding, optical fibres use total internal reflection to transmit information via light, maintaining performance even when bent.

General Wave Properties

• Waves transfer energy without transferring matter; particles oscillate around a fixed point.
• Key terms: Amplitude (max displacement from equilibrium), Wavefront (points on wave in cycle), Frequency (waves per second), Wavelength (distance between two points), Time period (duration of one wave).

Wave Speed and Relationships

• Wave speed equation: v = frequency × wavelength.
• Frequency relates to time period: f = 1/T.

The Doppler Effect

• A change in observed frequency and wavelength occurs when a wave source moves relative to an observer (e.g., a siren changing pitch when passing).

Electromagnetic Spectrum

• Key categories in order: Radio waves, Microwaves, Infrared, Visible light (ROYGBIV), Ultraviolet, X-rays, Gamma rays.
• All electromagnetic waves travel at high speeds in a vacuum.

Uses and Hazards of Electromagnetic Waves

• Radio waves: Communication (TV/radio), reflected by the ionosphere.
• Microwaves: Cooking and satellite transmissions; penetrate materials effectively.
• Infrared: Heaters and night vision technology.
• Visible Light: Fibre optics and photography.
• Ultraviolet: Fluorescent lamps and tanning.
• X-rays: Medical imaging and security; can penetrate materials.
• Gamma radiation: Food and medical equipment sterilization.
• Hazards: Microwaves cause internal heating, infrared leads to burns, ultraviolet raises skin cancer risk.

Sound Wave Properties

• Audible range for humans is 20 Hz to 20,000 Hz.
• Speed of sound can be measured by timing the echo of a sound made at a distance from a wall: speed = distance/time.
• An oscilloscope connected to a microphone can display sound waves, showing frequency and amplitude relationship: greater amplitude = louder sound, greater frequency = higher pitch.