Waves and Ray Optics

Single mechanical vibration

Produces a single oscillation or a wave pulse

Wave

A continuous stream of regular disturbances

Pulse

A single disturbance that propagates from one point to a next

Transverse wave

One in which the particles of the wave oscillate at right angles to the direction of travel of the wave (perpendicular to its propagation and travel in crests and troughs)

Longitudinal wave

One in which the particles of the wave oscillate in the same direction of travel of the wave (parallel to its propagation and travel in compressions and rarefactions)

Progressive wave

A wave produced as a result of oscillations and transfers energy from one location to another

Stationary wave

Formed by the superposition of two progressive waves of the same type, of equal amplitude and frequency traveling in opposite directions

Wavelength

The distance between two successive crests or two successive troughs or two successive points in phase

Displacement

The distance moved in a stated direction from the equilibrium position

Amplitude

Defined as the maximum displacement from the equilibrium position

In phase

When the distance between points in a progressive wave along the direction of propagation is equal to a whole number of wavelengths, the points have the same displacement, direction and speed in their vibrations

Out of phase / anti phase

When the distance between points in progressive wave along the direction of propagation is equal to ½ or 1 ½ etc

Period

The time taken for one complete oscillation

Frequency of a wave

The number of oscillations per second

Speed of a wave

The distance travelled by the wave per unit time

Electromagnetic waves

Consist of oscillating electric and magnetic fields at right angles to each other

Wavefront

A line perpendicular to the direction of propagation of the wave joining points which are in phase with each other

Wave equation

v = λf

Infrasound

Frequency below 20Hz

Audible range

Frequency 20Hz to 20kHz

Ultrasound

Frequency above 20kHz

Uses of ultrasound

Communicating, measuring distance, diagnostic imaging, materials testing, cleaning

Evidence sound waves reflect

Echoes

Evidence sound waves refract

Sounds are more audible at night

Evidence sound waves diffract

Music heard through a open window of a cabin

Evidence that sound waves interfere

Person walking parallel to loudspeaker hearing sound at not hearing sound at certain points

Diffraction

The spreading out of waves as it passes through a gap or past the edge of an object

How are sound waves produced

By mechanical vibrations

Refraction (waves)

the change in direction of a wave when it passes between two different media as a result of a change in speed

The principle of superposition

When two or more waves arrive at a point, the resultant displacement is the algebraic sum of the displacements of each wave

Interference of waves

Occurs when two similar waves pass through each other

Constructive interference

Occurs when waves are in phase and crests or troughs coincide

Destructive interference

Occurs when waves are out of phase and cancel each other

Law of reflection 1

The angle of incidence is equal to the angle of reflection

Law of reflection 2

The incident ray, the reflected ray and the normal all lie in the same plane

Law of refraction 1

Snell's Law

Snell's Law

States that the ratio of sin(i) to sin(r) is equal to a constant known as the refractive index, n

Law of refraction 2

The incident ray, refracted ray and the normal all lie on the same plane

Critical angle

The angle for which the angle of refraction is 90 degrees for a ray or wave traveling from a dense medium to a less dense medium

Condition 1 for total internal reflection

The wave must be traveling from a dense medium to a less dense medium

Condition 2 for total internal reflection

The angle of incidence at the boundary must be greater than the critical angle

Principal axis

Horizontal line drawn through the centre of the lens

Focal point (principal focus) of a converging lens

The point at which rays parallel to the principal axis converge

Reflection

Occurs when light leaves the object and is incident on a reflecting surface at a point of incidence, it then bounces off from the reflecting surface within the same medium as the object and enters the eye of the observer

Refraction

The bending of light as it leaves one medium and enters another with a different optical density