Year 9 Science - Waves

Flashcards of key vocabulary related to the topic of waves, including sound waves, light waves, reflection, refraction, lenses, and the human eye.

Vibration

A rapid back and forth motion.

Medium

The material a sound wave travels through.

Compression

A region along the wave where particles in the medium have been squeezed closer together.

Rarefaction

A region along the wave were particles in the medium have been stretched further apart.

Wavelength (𝝀)

The distance between two consecutive compressions, measured in metres (m).

Frequency (𝒇)

The number of times the particles in a wave vibrate each second; or the number of cycles the wave completes each second; measured in cycles per second (cps), or hertz (Hz).

Pitch

How high or low a sound sounds, which depends on frequency.

Amplitude

The maximum distance a particle in the wave moves from its resting position.

Loudness

How intense someone perceives a sound to be; depends on both the amplitude and the frequency of the waves.

Longitudinal Wave

A type of wave in which vibrations are parallel to the direction of wave travel.

Echo

A reflected sound wave that is heard as a distinct sound.

Reverberation

A hollow sound produced by multiple echoes running together.

Transverse Wave

A type of wave in which vibrations are perpendicular (at right angles) to the direction of wave travel.

Crest (peak)

The highest parts of a wave.

Trough

The lowest parts of the wave.

Electromagnetic Radiation (EMR)

Electromagnetic radiation that travels through the vacuum of space; all forms are called 'light'.

Speed of Light (𝑐)

The speed at which electromagnetic waves travel (𝑐 = 300 000 km/s in a vacuum).

Photon

Tiny packet of energy emitted when excited electrons lose energy or when any charged particle is accelerated.

Electromagnetic Spectrum

The complete range of electromagnetic waves placed in order of increasing frequency.

Transparent

Materials which allow light to pass through, with minimal scattering, allowing clear shapes to be seen through them.

Translucent

Materials that allow some light to pass through, but scatter most of it and therefore do not allow clear shapes to be seen through them.

Opaque

Materials that do not transmit light; light is either absorbed or reflected and cannot pass through.

Luminous

Materials that give off (or emit) the light they produce.

Non-luminous

Materials that do not emit their own light and can only be seen by the light they reflect.

Incandescent

Materials which emit light as a result of being heated.

Reflection

The bouncing back of a wave when it strikes a barrier.

Regular (specular) Reflection

Occurs when light is reflected off a very smooth surface, producing a clear, sharp image.

Irregular (diffuse) Reflection

Occurs when light is scattered in different directions when reflected off a rough surface, scattering them in different directions, and no (clear) image is produced.

Plane Mirror

A flat mirror.

Normal

A line drawn perpendicular (90o) to a surface or boundary where a ray strikes it .

Incident Ray

Incoming ray that strikes a surface.

Reflected Ray

Ray that bounces off a surface.

Angle of Incidence

The angle between the incident ray and the normal .

Angle of Reflection

The angle between a reflected ray and the normal .

Law of Reflection

The angle of incidence is equal to the angle of reflection, i=r.

Laterally Inverted

The image is flipped left to right, but it is not upside down.

Image Distance

The distance from Q to the same point on the plane mirror.

Virtual Image

Rays of light only appear to come from position of the image; light doesn't come from here.

Magnified

Larger than the object.

Diminished

Smaller than the object.

Upright

Right-side-up.

Inverted

Upside down.

Field of View

The amount of the surrounding area that can be seen in the mirror.

Concave Mirror

Causes light rays to converge, i.e. come together.

Converge

To come together.

Convex Mirror

Cause light rays to diverge, i.e. spread apart.

Diverge

To spread apart.

Focus (focal point)

A point where rays of light meet.

Focal Length

The distance from mirror to the focus, the point where the light rays cross/appear to cross.

Virtual Focus

Appears to converge behind the mirrors; light rays do not actually pass through this point; they only appear to do so

Real Image

Can be projected onto a screen; images where light rays actually meet.

Refraction

The bending of light as it passes from one medium into another; distorts the appearance of images.

Refractive Index

Measures the optical density of a substance, and can be used to calculate the angles.

Refracted ray

The refracted ray.

Angle of refraction

The angle of refraction.

Apparent Depth

Because refraction changes the direction of the light rays that enter our eyes to form an image, it tricks us into seeing objects differently; can give us a false sense of position.

Deviated

Turned away from; diverted.

Dispersion

The spreading of white light into an infinite range of colours and shades.

Primary Colors

Red, green and blue.

Secondary Colors

Yellow, cyan, and magenta.

Transmit

Allow to pass through.

Lens

A curved piece of transparent material, such as glass or plastic.

Biconvex Lens

Thicker in the middle; parallel rays focus; and.

Biconcave Lens

Thinner in the middle; parallel rays diverge.

Total Internal Reflection (TIR)

Occurs when light passes from a denser medium (where light travels slower) to a less dense medium (where light travels faster); and the angle of incidence must be greater than the critical angle (𝑖 > 𝑐); all of the incoming light is reflected

Critical Angle

The angle of incidence between the ray and the normal when it produces a ray refracted at 90o.

Optical Fibre

Use TIR to transmit data at the speed of light (including NBN).

Binocular Vision

Provides depth perception, i.e. gives us the ability to judge distances.

Cornea

Transparent outer covering of the eye that helps focus the light by refracting it.

Pupil

Black circular opening in the center of the iris, which is the coloured part of the eye; adjusts in size to control the amount of light entering the eye.

Lens

Biconvex lens, which further refracts the light and focuses it onto the retina at the back of the eye.

Retina

A layer of light-sensitive cells at the back of the eye (rods and cones) that convert the light into electrical signals.

Optic Nerve

A bundle of nerve fibres, to the brain where the signals are processed and interpreted to form images.

Accommodation

Process where the lens changes shape to focus on objects at different distances

Myopia (short-sightedness)

Caused by the eyeball being too long and the focus of the image falling in front of the retina; nearby objects are clear; distant objects are blurry.

Hyperopia (long-sightedness)

Caused by the eyeball being too short and the focus of the image falling behind the retina; distant objects are clear; nearby objects are blurry.

Astigmatism

The distortion of images caused by the cornea not having perfectly spherical curvature.

Presbyopia

The loss of the eye’s ability to accommodate (change focus) to see images that are very close or very far, caused by a loss in elasticity of the lens due to aging.

Cataracts

A medical condition in which the lens becomes progressively opaque (cloudy white).

Colour-blindness

A condition where a person has difficult distinguishing certain colours.