Wave Physics and the EM Spectrum

Flashcards covering the basics of wave properties, experiments, reflection, refraction, the electromagnetic spectrum, and lenses based on the lecture transcript.

Waves

Phenomena that transfer energy from one place to another without transferring any matter.

Amplitude

The displacement from the rest position to a crest or trough.

Wavelength

The length of one full cycle of a wave, such as the distance from crest to crest or compression to compression.

Frequency

The number of complete waves or cycles passing a certain point per second, measured in hertz ($Hz$).

Hertz ($Hz$)

The unit of frequency where $1\,Hz$ is equal to $1$ wave per second.

Period

The number of seconds it takes for one full cycle to complete, calculated as $\text{Period} = 1 \div \text{frequency}$.

Transverse Waves

Waves where vibrations are perpendicular ($90^{\circ}$) to the direction of wave travel, such as all electromagnetic waves and water ripples.

Longitudinal Waves

Waves where vibrations are parallel to the direction of wave travel, creating compressions and rarefactions, such as sound waves and P waves.

Wave Speed Equation

$$\text{wave speed (m/s)} = \text{frequency (Hz)} \times \text{wavelength (m)}$$

Normal

An imaginary dotted line at right angles ($90^{\circ}$) to a surface at the point where a wave hits it.

Law of Reflection

The rule stating that the angle of incidence is always equal to the angle of reflection.

Specular Reflection

Reflection in a single direction by a smooth surface, such as a mirror, creating a clear reflection.

Scattering

Reflection off a rough surface where waves are reflected in all directions because the normal is different for each incident ray.

Refraction

The bending of a wave when it crosses a boundary between materials of different densities, caused by a change in speed.

Audition (Human Hearing Range)

The range of frequencies humans can hear, which is approximately $20\,Hz$ to $20\,000\,Hz$ for young people.

Ultrasound

Sound with frequencies above $20\,kHz$, used in medical imaging and industrial flaw detection.

Sonar

A system used by boats and submarines to find the distance to the seabed using the reflection of sound pulses.

Electromagnetic (EM) Waves

A continuous spectrum of transverse waves that travel at the same speed ($velocity$) through air or a vacuum.

Ionising Radiation

High-frequency EM waves like UV, X-rays, and gamma rays that transfer enough energy to knock electrons off atoms, potentially causing cancer.

Radio Waves

EM waves used for communication, created by oscillating charges in alternating current ($a.c.$) circuits.

Optical Fibres

Thin glass fibers that carry data over long distances as pulses of light by reflecting them off the sides of a narrow core.

Fluorescence

A property where chemicals absorb ultra-violet (UV) radiation and kemudian emit visible light.

Radiotracers

Radioactive isotopes swallowed or injected into a patient that emit gamma rays to be detected outside the body for medical imaging.

Opaque

Materials that do not transmit light; they absorb some wavelengths and reflect others to determine their color.

Primary Colours (of Light)

Pure red, green, and blue, which cannot be made by mixing other light colors.

Colour Filters

Objects used to filter out particular wavelengths of light, only transmitting certain colors and absorbing the rest.

Convex (Converging) Lens

A lens that bulges outwards, causing parallel rays of light to converge at a principal focus.

Concave (Diverging) Lens

A lens that caves inwards, causing parallel rays of light to spread out from a virtual principal focus.

Principal Focus

The point where rays hitting the lens parallel to the axis meet (convex) or appear to come from (concave).

Focal Length

The distance from the centre of the lens to the principal focus.

Real Image

An image formed where light rays from an object actually come together and can be captured on a screen.

Virtual Image

An image formed when light rays are diverging, making it appear that the light comes from a different place.

Short-sightedness

A condition where distant objects are focused in front of the retina, corrected using a concave lens.

Long-sightedness

A condition where near objects are focused behind the retina, corrected using a convex lens.