Waves

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38 Terms

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Longitudinal wave

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

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Transverse wave

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

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Amplitude

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

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Wavefront

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

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Frequency (+ units)

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

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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)

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Time period

The time it takes for the source to produce one wave

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What waves do and do not transfer

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

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Equation for wave speed

Speed = frequency x wavelength

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Equation for frequency

Frequency = 1 / time period

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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.

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Light waves: longitudinal or transverse?

Transverse

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Properties of light waves

They can be reflected and refracted (all waves can)

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

N = sin(i) / sin(r)

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What happens when a light wave enters a denser medium?

It bends/refracts towards the normal

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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.

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Equation: critical angle and refractive index

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

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Sound waves: longitudinal or transverse?

Longitudinal

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Frequency range of human hearing

20-20000 Hz

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Ultrasound

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

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Relationship between frequency and pitch

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

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Relationship between amplitude and volume

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

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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)

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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

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Frequency range for human hearing

20 - 20000 Hz

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The electromagnetic spectrum (longest to shortest wavelength)

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

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

The same

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Violet - longest or shortest wavelength?

Shortest

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Uses of radio waves

Broadcasting and communications

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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

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Uses of infrared, dangers

Used for night vision equipment; risk of skin burns

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Uses of visible light

Optical fibres and photography

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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.

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Uses of x-rays

Observing the internal structure of objects, including for medical purposes

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Uses of gamma rays

Sterilising medical equipment and food

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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.

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Electromagnetic spectrum waves

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

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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