(K) Unit 22 Waves

Angle of incidence

Angle between the normal and the incident ray

Angle of reflection

The angle between the reflected ray and the normal (the imaginary line drawn at 90 degrees to the reflecting surface).

Critical angle

The minimum angle at which total internal reflection takes place.

Density

Is the ratio of mass to volume. It is usually measured in kilograms per metre cubed (kg/m3 ) or grams per centimetre cubed (g/cm3 ).

Diffuse reflection

When light is reflected off a surface and is scattered in different directions.

Dispersion

Spreading out of the different wavelengths of light, caused by refraction of light as it passes through a prism.

Electromagnetic wave

A transverse wave propagated by variations (oscillations) of electric and magnetic field strengths.

Electromagnetic spectrum

Range of all possible frequencies of electromagnetic radiation, e.g. ultraviolet light is part of the EM spectrum.

Frequency

The number of waves produced each second. The unit of frequency is hertz (Hz)

Incident ray

Light ray moving towards a surface or boundary.

Ionising radiation

Radiation that is able to remove electrons from atoms or molecules to produce positively charged particles called ions.

Law of reflection

In reflection at a surface, the angle of incidence equals the angle of reflection.

Lens

A transparent tool that can change the direction of a ray of light.

Longitudinal wave

A wave that moves in the same direction as the direction in which the particles are vibrating

Matter

Sub-atomic particles and anything made from them, such as atoms and molecules, are matter. Energy and forces are not matter.

Medium

A material through which a wave can be transmitted (propagate).

Normal

A line that is drawn at an angle of 90° to a surface or boundary.

Opaque

Not transparent or see-through.

Optical fibre

A fine glass fibre, through which light travels by total internal reflection, from one end to the other.

Oscillations

The repeated and regular fluctuations, above and below the same position, eg the pressure of a sound wave or the voltage of an alternating current.

Plane

A flat, two-dimensional surface.

Ray diagram

Diagram that represents the direction and angle of travel of light.

Radiation

Energy transferred as a wave spreading out from a source - eg light, infrared, sound.

Reflected ray

Is the ray that represents the light reflected by a surface (or boundary).

Refracted

A ray (wave) that changes speed and direction when it enters a medium of different density

Refraction

Process by which a wave changes speed and sometimes direction upon entering a denser or less dense medium, e.g. a light ray changes direction when refracted by a glass block.

Retina

The light-sensitive area on the back of the eye. Light must be focused on the retina in order to see clearly.

Specular reflection

Reflection in which light travelling towards a surface in one direction is all reflected in a single direction.

Spectrum

A series of similar waves arranged in order of wavelength or frequency.

Translucent

Allows light to pass through but is not completely clear.

Transparent

Able to be seen through

Transverse (motu hake)

At 90 degrees. In transverse waves, the vibrations are at 90 degrees to the direction in which the waves travel.

Transverse wave

A wave that moves in a direction at right angles to the way in which the particles are vibrating.

Total internal reflection (whakaata a-roto)

Complete reflection of a light ray reaching a boundary at an angle of incidence greater than the critical angle.

Transmitted (tare)

A wave is passed across or through a material (medium), e.g. light waves are transmitted through air, glass and water.

Vacuum (korehau)

A volume that contains no matter.

Vibrations (ngatere)

Repeated movements back and forth (about a fixed point).

Virtual image (mātātuhi mariko)

An image from which rays of light appear to come but do not do so in reality.

Waves (karekare)

Vibrations that transfer energy from place to place without the transference of matter.

Wavelength (roangaru)

The length of a single wave, measured from one wave peak to the next