Waves

Longitudinal wave

Longitudinal wave

A wave in which the particles oscillate parallel to the direction of energy flow

Transverse wave

A wave in which the particles oscillate perpendicular to the direction of energy flow

Amplitude

The maximum movement of particles from their equilibrium position in a wave

Wavefront

An imaginary surface representing corresponding points of a wave that vibrate in unison

Frequency (+ units)

The number of waves produced per second, measured in Hertz (Hz)

Wavelength

The distance between a particular point on one wave, and the same point on the next wave (e.g. crest to crest, or trough to trough)

Time period

The time it takes for the source to produce one wave

What waves do and do not transfer

Do: transfer energy and information. Do not: transfer matter.

Equation for wave speed

Speed = frequency x wavelength

Equation for frequency

Frequency = 1 / time period

The Doppler effect

If the source of the wave is moving away from you, the wavefronts will be become further apart, the wavelength of the wave will appear to become longer, and the frequency will appear to decrease, so the pitch of the waves will appear to be lower. The opposite is true if the source is moving towards you.

Light waves: longitudinal or transverse?

Transverse

Properties of light waves

They can be reflected and refracted (all waves can)

Equation: refractive index, angle of incidence and angle of refraction

N = sin(i) / sin(r)

What happens when a light wave enters a denser medium?

It bends/refracts towards the normal

Critical angle (c)

If the angle of incidence of a light wave going from a more to less dense medium is equal to the critical angle, it is refracted at 90 degrees. If the angle of incidence is smaller than the critical angle, refraction occurs, and if it is greater than the critical angle, total internal reflection occurs.

Equation: critical angle and refractive index

Sin(c) = 1/n or n = 1/sin(c)

Sound waves: longitudinal or transverse?

Longitudinal

Frequency range of human hearing

20-20000 Hz

Ultrasound

A sound with a frequency over 20000 Hz, that is inaudible to human hearing

Relationship between frequency and pitch

The higher the frequency of the vibrations from the source, the higher the pitch

Relationship between amplitude and volume

The higher the amplitude of the vibration of the source, the louder the sound is

Uses of total internal reflection

In optical fibres - endoscopes and fibre optic cables; and with reflecting prisms - in bicycle reflectors, cats eyes, and periscopes (two prisms)

When does total internal reflection occur?

When the angle of incidence is greater than the critical angle, and when light it travelling from a more dense to a less dense medium

Frequency range for human hearing

20 - 20000 Hz

The electromagnetic spectrum (longest to shortest wavelength)

radio waves, microwaves, infrared light, visible light, ultraviolet light, x-rays, gamma rays

Speed of all electromagnetic spectrum waves in free space / a vacuum

The same

Violet - longest or shortest wavelength?

Shortest

Uses of radio waves

Broadcasting and communications

Uses and dangers of (and preventative measures against) microwaves

Used for cooking and satellite communications; danger of internal heating of body tissue; microwave ovens have metal grids in the doors and metal walls to prevent microwaves from escaping and causing harm

Uses of infrared, dangers

Used for night vision equipment; risk of skin burns

Uses of visible light

Optical fibres and photography

Uses, dangers, prevention of ultraviolet

Used for fluorescent lamps; danger of damage to eyes or blindness and damage to surface cells, causing premature aging or skin cancer. Sunglasses and sunscreen will absorb it.

Uses of x-rays

Observing the internal structure of objects, including for medical purposes

Uses of gamma rays

Sterilising medical equipment and food

Dangers of x-rays and gamma rays, prevention

Ionising radiation - they can penetrate the body and cause internal damage, and can cause genetic mutations which can lead to cancer. Doctors limit their exposure to x-rays, and low levels of the x-rays are used for safety. Radiation badges can be worn to monitor the levels of gamma radiation one is exposed to.

Electromagnetic spectrum waves

Transverse waves that transfer energy from the source of the waves to an absorber

Shared properties of electromagnetic spectrum waves

They are all transverse, they all can travel through a vacuum, they all travel at the same speed through a vacuum