Topic 4 + 9 - Waves

Simple harmonic motion (SHM)

An object undergoes SHM when its acceleration is proportional and opposite to the displacement from equilibrium: a ∝ -x²

Longitudinal wave

A wave in which the energy transfer is parallel to the oscillations defining the wave.

Transverse wave

A wave in which the energy transfer is perpendicular to the oscillations defining the wave.

The principle of superposition

When two waves overlap, the net displacement at any point is the sum of the individual displacements of each wave.

Standing waves

Two identical waves traveling in opposite directions can superpose and create a resultant wave with some points that are not moving (nodes) and some points with maximum amplitude (antinodes). There is no overall energy transfer in a standing wave (the energy is trapped between the nodes).

Polarized light

Light is polarized when the electric field of an electromagnetic wave oscillates in one direction (\= linearly polarized).
Note: Polarization is a property of transverse waves only. E.g. sound waves cannot be polarized.

Unpolarized light

Light is unpolarized when it contains light polarized in many different directions.

Doppler Effect

When there is a change in the observed frequency of a wave as a result of relative motion between the source and an observer

Rayleigh Criterion

Two images are just resolved when the first minimum of the first diffraction pattern coincides with the maximum of the second pattern.

Drawing a Single

Slit Diffraction Pattern

Distinguish between polarised and unpolarised light

• in unpolarized light the electric field vector may vibrate in any plane (normal to the direction of propagation);

• in polarised light the vector/electric field vibrates in one plane only;

Why doppler effect occurs

• Speed of sound relative to observer is different

• Wavelength unchanged to frequency changes