Waves - Revision

Waves transfer [blank_start]energy[blank_end] from one place to another. Oscillations in a longitudinal wave are [blank_start]parallel[blank_end] to the direction of energy transfer. Oscillations in a transverse wave are [blank_start]perpendicular[blank_end] to the direction of energy transfer. Sound waves are [blank_start]longitudinal[blank_end], electromagnetic waves are [blank_start]transverse[blank_end] and mechanical waves (e.g. on a slinkly spring) can be either [blank_start]trasnverse[blank_end] or [blank_start]longitduinal[blank_end].

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The number of waves that pass in one second is called the wave [blank_start]frequency[blank_end], measured in [blank_start]Hertz[blank_end] ([blank_start]Hz[blank_end]). The amplitude of a wave goes from the [blank_start]center[blank_end] to the [blank_start]top[blank_end], while the wavelength goes from [blank_start]peak[blank_end] to [blank_start]peak[blank_end].

Light of a single frequency is described as [blank_start]monochromatic[blank_end].

The speed of a wave can be found using the equation: [blank_start]v[blank_end] = [blank_start]f[blank_end] x [blank_start]lambda[blank_end] v = [blank_start]speed[blank_end] (units: [blank_start]m/s[blank_end]) f = [blank_start]frequency[blank_end] (units: [blank_start]Hz[blank_end]) λ = [blank_start]wavelength[blank_end] (units: [blank_start]m[blank_end])

A radio station transmits radio waves at a frequency of 2 x 10^5 Hz. The speed of radio waves is 3.0 x 10^8 m/s. Calculate the wavelength of the radio waves. To answer the question, you must use the formula [blank_start]v[blank_end] = [blank_start]f[blank_end] x [blank_start]lambda[blank_end]. The answer to the question is: [blank_start]1500 m[blank_end]

The electromagnetic spectrum is a family of waves which can all: 1) Travel at the speed of [blank_start]light[blank_end] (about [blank_start]3 x 10^8 m/s[blank_end]) 2) Travel through a [blank_start]vacuum[blank_end] (empty space - no medium required!) 3) Transfer [blank_start]energy[blank_end] from one place to another.

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The higher the frequency (the [blank_start]smaller[blank_end] the wavelength) of electromagnetic radiation, the more [blank_start]energy[blank_end] it transfers. This is why [blank_start]gamma[blank_end] rays (from radioactive material), x-rays (used in [blank_start]hospitals[blank_end]), and [blank_start]ultraviolet[blank_end] radiation (from the sun) can be harmful to living tissue.

State the safety issues regarding the use of microwaves and x-rays: Microwaves: can [blank_start]heat[blank_end] up body [blank_start]tissue[blank_end], damage [blank_start]living[blank_end] [blank_start]cells[blank_end] X-Rays: can cause [blank_start]ionization[blank_end], kill [blank_start]living[blank_end] [blank_start]cells[blank_end], cause [blank_start]cancerous[blank_end] changes

[blank_start]Microwave[blank_end] radiation and [blank_start]radio[blank_end] waves are able to penetrate your skin. Their energy can be [blank_start]absorbed[blank_end] by body tissue, which can [blank_start]heat[blank_end] internal organs and may damage them. [blank_start]Infra-red[blank_end] radiation from the sun is absorbed by your [blank_start]skin[blank_end]. Too much of this can cause [blank_start]burns[blank_end].

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Describe the uses of these electromagnetic waves: Radio Waves: r[blank_start]adio[blank_end] [blank_start]communication[blank_end] Microwaves: s[blank_start]atellite[blank_end] [blank_start]communication[blank_end], m[blank_start]obile[blank_end] [blank_start]phone[blank_end] [blank_start]networks[blank_end], h[blank_start]eating[blank_end] Infra-red: r[blank_start]emote[blank_end] [blank_start]controls[blank_end], i[blank_start]ntruder[blank_end] [blank_start]alarms[blank_end], o[blank_start]ptical[blank_end] [blank_start]fibre[blank_end], r[blank_start]adiant[blank_end] [blank_start]heating[blank_end] X-Rays: m[blank_start]edicine[blank_end], a[blank_start]irport[blank_end] [blank_start]security[blank_end]

If a wave source (such as [blank_start]light[blank_end] from a distant galaxy, or [blank_start]sound[blank_end] from a passing ambulance) moves away from an observer, the observed wavelength [blank_start]increases[blank_end] and the frequency [blank_start]decreases[blank_end]. This is known as the [blank_start]Doppler[blank_end] effect. If the wave source moves towards the observer, the complete [blank_start]opposite[blank_end] happens. The wavelength [blank_start]decreases[blank_end], while the frequency [blank_start]increases[blank_end].

There is an observable increase in the [blank_start]wavelength[blank_end] of light from most [blank_start]distant[blank_end] galaxies. The further away the galaxies are, the [blank_start]greater[blank_end] the observed increase in [blank_start]wavelength[blank_end], and so the [blank_start]faster[blank_end] they are moving away from us. This effect is called [blank_start]red shift[blank_end] because the wavelengths are stretched towards the red end of the spectrum.

Name four types of mechanical waves: w[blank_start]ater[blank_end] [blank_start]wave[blank_end] [blank_start]waves[blank_end] on a s[blank_start]pring[blank_end] s[blank_start]ound[blank_end] [blank_start]wave[blank_end] e[blank_start]arthquake[blank_end] [blank_start]wave[blank_end] w[blank_start]ater[blank_end] [blank_start]waves[blank_end] are t[blank_start]ransverse[blank_end] [blank_start]waves[blank_end] on a s[blank_start]pring[blank_end] can be l[blank_start]ongitudinal[blank_end] or t[blank_start]ransverse[blank_end] s[blank_start]ound[blank_end] [blank_start]waves[blank_end] are l[blank_start]ongitudinal[blank_end] e[blank_start]arthquake[blank_end] [blank_start]waves[blank_end] can be l[blank_start]ongitudinal[blank_end] (p[blank_start]ressure[blank_end] wave) or t[blank_start]ransverse[blank_end] (e[blank_start]arth[blank_end] wave)

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Sound is caused by [blank_start]vibrations[blank_end] which make pressure waves move through a substance (such as air). In a sound wave, particles oscillate [blank_start]parallel[blank_end] to the direction of the wave motion. A sound wave is therefore a type of [blank_start]longitudinal[blank_end] wave.

The hearing frequency of an average human is [blank_start]20[blank_end]Hz - [blank_start]20kHz[blank_end].

In a sound wave: Pitch depends on the wave's [blank_start]frequency[blank_end]. Loudness depends on the wave's [blank_start]amplitude[blank_end]. Echoes are caused when the wave [blank_start]reflects[blank_end] off an object.

Sound waves need a [blank_start]medium[blank_end] (a material) to travel through (they cannot travel through a [blank_start]vacuum[blank_end]). Describe a simple experiment to determine the speed of sound in air: • Stand 100m away from a brick [blank_start]wall[blank_end] • [blank_start]Clap[blank_end] your hands • Use a [blank_start]stopwatch[blank_end] to measure the time taken between you clapping your hands and the [blank_start]echo[blank_end] returning to you • [blank_start]Retake[blank_end] the experiment at least [blank_start]3[blank_end] times • Use the formula [blank_start]s[blank_end] = [blank_start]d[blank_end]/[blank_start]t[blank_end] to calculate the [blank_start]average[blank_end] [blank_start]speed[blank_end]

What are some typical values of the speed of sound in: Gases: [blank_start]330[blank_end] m/s Liquids: [blank_start]1500[blank_end] m/s Solids: [blank_start]5200[blank_end] m/s