3 Waves and Optics

Waves

Oscillations that transfer energy not matter.

Transverse waves

Doesn’t require a medium to propagate, with oscillations perpendicular to the direction of travel.

Amplitude (A)

Maximum Displacement from equilibrium.

Wavelength (λ)

Length of one wave cycle.

Time Period (T)

Time for one wave.

Frequency (f)

How many waves a second.

Wave Speed (c)

Speed of wave.

In Phase

Refers to two or more waves that have the same frequency and phase, resulting in constructive interference.

Out of Phase

Refers to two or more waves that have a phase difference of 180 degrees, resulting in destructive interference.

Phase Difference

Depends on the fraction of wavelength

Path Difference

The difference between two sources of light measured in wavelengths.

Longitudinal Waves

Oscillates parallel to the direction of transfer of energy. Requires a medium to travel

Polarization

Restricts the oscillations of a wave to one plane.

Refraction

When light passes between mediums the light changes direction.

Total Internal Reflection

When the angle of incidence exceeds the critical angle, causing light to be completely reflected back into the medium.

Critical Angle

The angle of incidence at which light refracts by 90 degrees.

Optical Fibres/Fibre Optics

Thin flexible piece of glass.

Material (Chromatic) Dispersion

Different wavelengths travel at different speeds in the same medium.

Modal (Multi-path) Dispersion

Caused by the pules taking different routes down the fibre, causes pulse broadening

Diffraction

When a wave passes through a gap they spread out.

Coherence

Waves are at the same frequency and have a constant phase difference.

Superposition

Process which two waves combine into a single wave when they overlap.

Constructive Interference

Creates a resultant wave with large amplitude.

Destructive Interference

Creates a resultant wave with small or 0 amplitude.

Double Slit Interference

Special case of superposition due to light traveling through 2 splits

Young's Double Slit Experiment

Showed the interference of light and proved light is a wave

Pattern of the double slit

A series of symmetric equally spaced bright and dark fringes about a central bright fringe which is directly behind the midpoint

Intensity of the light from a double slit

Decreases as distance from the centre increases

Central Bright Fringe

The brightest fringe in the interference pattern

Other Bright Fringes

Fringes that are bright but not the central one

Dark Fringes

Fringes that are not visible due to destructive interference

Single Slit Interference

Wide central maxima with a width twice that of the other maxima and the brightest

Diffraction Gratings

Series of narrow, parallel slits usually around 500 slits per mm

Zero-order Maximum

The first bright line directly behind the grating

First Order Maximum

The bright line at an angle θ from the zero-order maximum

Standing Waves

Two waves with the same frequency traveling in different directions will superpose to form a standing wave

Nodes

Positions on a standing wave where the amplitude is zero or very small

Anti-nodes

Positions on a standing wave where the amplitude is maximum

Harmonics

Increasing frequency causes different harmonics, with the first standing wave formed being the fundamental harmonic