Waves

Front 1

What are the different categories of waves?

Back 1

In transverse waves, each particle oscillates perpendicular to the direction of propagation with no horizontal movement.

Particles in longitudinal waves oscillate parallel to the direction of propagation, with no vertical movement. There are regions were particles are close together (compression) and far apart (rarefaction).

Front 2

Give example of the types of waves?

Back 2

Mechanical waves are the oscillation of particles in a physical vacuum, which can either be transverse or longitudinal. E.g. sound waves, earthquarke P and S waves, and water waves.

Electromagetic (EM) waves are produced by the acceleration of charged particles, and, unlike mechanical waves, can transmit energy through a vacuum. They are always transverse waves. E.g. microwaves, X-rays, and visible light.

Front 3

Describe an Electromagnetic wave?

Back 3

Electromagetic (EM) waves are distrubances in electrical and magnetic fields, which are perpendicular to each other. They are the only waves to travel through a vacuum.

Front 4

Describe a string wave?

Back 4

String waves on guitar and violin strings occur when the string is plucked.

Front 5

Describe a water wave?

Back 5

Water waves occur whenever the surface of the water gets disturbed. They are mechanical transverse waves.

Front 6

What are Earthquake S (secondary) waves?

Back 6

Earthquake S (secondary) waves are produced in the Earth by movement of the crust, and displace the ground at right angles toqards propagation. Most devistation is caused by this wave, followed by another; surface waves.

Front 7

What are sound waves?

Back 7

Sound waves are mechanical waves generated by the vibration of particles of a solid, liquid or gas.

Front 8

What are Earthquake P (primary) waves?

Back 8

Earthquake P (primary) waves are produced by earthquakes, and alternately compress and stretch out the ground through which they travel. They are twice as fast as S waves (~5000-8000 m/s) and can travel through liquids. This helped determine the core is molten.

Front 9

What is meant by the amplitude of a wave?

Back 9

The amplitude is the maximum displacement of the wave in either the positive or the negative direction.

Front 10

What is wavelength?

Back 10

The wavelength of a wave is the distance between two identical points on consecutive cycles.

Front 11

What is one cycle?

Back 11

One complete cycle of a wave is equivalent to one wavelength.

When a wave hits a boundary it can't pass through, it reflects.

Front 12

What is the trough?

Back 12

The trough of a wave is the point of maximum negative displacement.

Front 13

What is the peak of a wave?

Back 13

The peak or crest of a wave is the point of maximum positive displacement.

Front 14

Where is the rest position of a wave?

Back 14

The equilibrium or rest position is the point at which the particles of wave remain in place when there is no disturbance.

Front 15

What is polarisation and how is it achieved?

Back 15

Polarisation occurs only in transverse waves. They can vibrate in any plane, 90° towards propagation. Plane-polarised light has all waves in the same plane, using a polarising filter. Plane of polarisation is parallel to the filter. Light passing through the second filter is proportional to the relative angles of the two filters. This is Malus's law.

Front 16

What is Malus's law?

Back 16

The intensity of polatised light through another filter is calculated:

(Initial intensity of light)(cos2(Angle))

Named after Étienne-Louis Malus, a French physician, mathematician and officer.

Front 17

How is polarisation used in the world?

Back 17

Used in sunglasses to reduce glare of semi-polarised reflected light, and by photographers to filter sunshine when taking photos. Stress analysis for certain plastics like Perspex. Polarised light micrography used to analyse crystal structures.

Front 18

What is the period of the wave?

Back 18

The period is the time (seconds) taken for a wave to peak to travel the distance of one wavelength. The frequency is the number of complete cycles per second (in hertz).

Front 19

What is meant by phase difference?

Back 19

Phase difference is the fraction of a complete cycle between two points on a wave. Particles one wavelength apart are in phase at 2π or 360°. Reflected waves undergo phase change of π radians or 180°.

Front 20

What is superposition?

Back 20

In superposition, the resultant displacement at a point is equal to the sum of the individual displacements when two or more waves overlap.