Electromagnetic Radiation and Wave Properties: Year 9 Physics Guide

Wave

A wave is a transfer of energy without the net transfer of matter.

Mechanical Waves

Mechanical waves need a medium to travel (propagate) through.

Electromagnetic Waves

Electromagnetic waves do not require a material medium.

Example of Mechanical Waves

Sound waves, which transfer sound energy through air (or another medium).

Oscillation

The movement of particles around their respective equilibrium positions without traveling with the wave.

Electromagnetic Wave Creation

A changing electric field produces a perpendicular changing magnetic field, which produces a changing electric field.

Charged Particle

A charged particle (like an electron) creates an electric field around it.

Effect of Acceleration on Electric Field

When a charged particle accelerates, the electric field around it starts to change.

Propagation of Fields

Changing electric and magnetic fields move outward through space.

Examples of Electromagnetic Waves

Light, microwaves, X-rays, and radio waves.

Emission of Electromagnetic Waves

An accelerating charged particle will emit electromagnetic waves.

Frequency of Electromagnetic Waves

The frequency of the electromagnetic wave will be equal to the frequency of the oscillation of the charged particle.

Speed of Electromagnetic Waves

All electromagnetic waves travel at the same speed in a vacuum, independent of frequency and wavelength.

Transverse Waves

The oscillations of particles in a transverse wave are perpendicular (90°) to the direction of wave propagation.

Examples of Transverse Waves

Waves in strings and springs.

Crests

The points where particles have maximum positive displacement.

Troughs

The points where particles have maximum negative displacement.

Longitudinal Waves

Waves where the oscillations of particles are parallel to the direction of wave propagation.

Compressions

The points where particles are most closely grouped together (under the most pressure) in a longitudinal wave.

Rarefactions

The points where particles are spread out (under the least pressure) in a longitudinal wave.

Amplitude

The magnitude of the maximum oscillation from the equilibrium position of a wave.

Energy of a wave

Dependent on the amplitude of the wave.

Wavelength

The distance between any two identical points in the wave, such as from one crest to the next crest.

Period

The time taken to complete one wave cycle, equivalent to the time for any point on the wave to travel one wavelength.

Frequency

The number of wave cycles completed per unit of time.

Pitch

For sound, increasing frequency corresponds to increasing pitch.

Electromagnetic radiation

Energy that travels as waves made of changing electric and magnetic fields, including light, radio waves, X-rays, and microwaves.

Electromagnetic Spectrum

The range of all types of electromagnetic waves, from those with the longest wavelengths and lowest energy (like radio waves) to those with the shortest wavelengths and highest energy (like gamma rays).

Visible light

The small region of the electromagnetic spectrum (wavelengths between 380 nm and 750 nm) that is visible to the human eye.

Radio Waves

Electromagnetic waves that travel long distances uninterrupted due to their long wavelength and can diffract around obstacles.

Microwaves

Electromagnetic waves used to cook food in microwave ovens by matching the resonant frequency of water molecules in food causing them to vibrate.

Polarising sunglasses

Sunglasses that filter out all but one plane of EM radiation waves to reduce glare.

Cosmic Microwave Background (CMB) Radiation

Electromagnetic radiation which was created in the early stages of the universe and continues to reach Earth, providing strong evidence for the Big Bang Theory.

Infrared

All objects emit electromagnetic radiation due to the thermal vibration of charged particles. When infrared radiation hits an object, it causes the particles in that object to vibrate so the object heats up. It is also used in some forms of signal transmission such as TV remote controls.

Ultraviolet

Used in sterilisation processes and to cure (harden) different materials due to its high energy. Used in black lights (UV light bulbs) for forensic analysis as it causes other substances, including bodily fluids, to fluoresce (emit visible light).

X-rays

High energy and highly penetrating. Useful for imaging bone structures as they pass easily through soft tissue. Can damage the DNA in cells or even kill cells in significant doses.

Gamma Rays

Higher energy, more penetrating, and more damaging than X-rays. Produced by nuclear reactions. Used in medicine to target and kill tumour cells but care must be taken to minimise damage to other cells.

UV

Needed for body's production of Vitamin D. Excess exposure can cause burns and damage to skin. Excess exposure can lead to skin cancer.

X-Rays (Uses)

Medical imaging of bones and soft tissues. X-ray scans at airports and other security points.

Gamma Rays (Uses)

Radiotherapy for cancers. PET scans (medical imaging).

Harmful Effects of X-rays

Damage to cells, tissues and DNA. Extended exposure can cause radiation poisoning.

Harmful Effects of Gamma Rays

Damage to cells, tissues and DNA.

Microwaves (Uses)

Used for mobile phone signals, Wi-Fi and radar systems.

Infrared (Uses)

Used in some forms of signal transmission such as TV remote controls.

Ultraviolet (Uses)

Sterilising foods and objects. Medical imaging and biomedical research.

Gamma Rays (Harmful Effects)

Care must be taken to minimise damage to other cells.

X-rays (Harmful Effects)

Targeted therapy (killing) of cancer cells.

Cosmic Objects

Produced by cosmic objects and used by astronomers to study those objects.

Mechanical wave

A wave that requires a medium to travel through.

Electromagnetic wave

A wave that can travel through a vacuum and does not require a medium.

Longitudinal wave

A wave in which the particles of the medium move parallel to the direction of the wave's travel.

Transverse wave

A wave in which the particles of the medium move perpendicular to the direction of the wave's travel.

Medium

The substance through which a wave travels.

Vibration

An oscillation or repetitive motion of a particle or wave.

Energy transfer

The movement of energy from one location to another.

Compression

A region in a longitudinal wave where particles are closer together.

Rarefaction

A region in a longitudinal wave where particles are further apart.

Direction of travel

The path along which a wave propagates.

Crest

The highest point of a wave.

Trough

The lowest point of a wave.

Equilibrium (normal)

The rest position of a wave, where there is no disturbance.

Wave speed

The speed at which a wave travels through a medium.

Electric field

A field around charged particles that exerts a force on other charged particles.

Magnetic field

A field around magnets and electric currents that exerts a force on other magnets and currents.

Ionising radiation

Radiation with enough energy to remove tightly bound electrons from atoms, creating ions.

Non-ionising radiation

Radiation that does not carry enough energy to ionise atoms or molecules.

Radiowaves

Electromagnetic waves with wavelengths longer than infrared light.

Infrared radiation

Electromagnetic radiation with wavelengths longer than visible light but shorter than microwaves.

Ultraviolet (UV) radiation

Electromagnetic radiation with wavelengths shorter than visible light but longer than X-rays.