Physics. 3 Waves

What type of wave is sound

Sound waves are longitudinal waves, which require a medium (solid, liquid, or gas) to travel through. They cannot travel through a vacuum.

How are longitudinal waves visually represented

They are drawn as parallel lines with compressions (lines close together) and rarefactions (lines spread apart). The wave travels parallel to the direction of energy transfer.

What are compressions and rarefactions in a sound wave

Compressions are regions of higher particle density and pressure. Rarefactions are regions of lower particle density and pressure.

What happens when a sound wave hits a solid object

The variations in pressure cause the solid's surface to vibrate in sync with the sound wave.

What is the approximate speed of sound in air

Between 330-350 m/s depending on temperature; higher temperature increases speed.

In which states of matter does sound travel fastest and slowest

Fastest in solids (5000 m/s) then liquids (1500 m/s) and slowest in gases (340 m/s).

How does frequency relate to pitch

Higher frequency = higher pitch; lower frequency = lower pitch.

How does amplitude relate to volume

Larger amplitude = louder volume; smaller amplitude = quieter volume.

What is an echo

The reflection of a sound wave off a hard surface.

Formula for distance to reflective surface using echo

distance = 1/2 x speed of sound x time for echo to return.

What is the frequency range of human hearing

Approximately 20 Hz to 20 000 Hz.

What is ultrasound

Sound with a frequency above 20 000 Hz (20 kHz) beyond human hearing.

Main uses of ultrasound

Medical imaging; non-destructive testing; sonar.

How is ultrasound used to detect cracks in metal

Ultrasound reflects off cracks; reflected pulses appear earlier on oscilloscope than end-of-object pulse.

How is depth calculated using ultrasound

depth = 1/2 x speed of ultrasound x time for echo to return.

Why is ultrasound considered safe for medical use

It is non-invasive and non-ionizing so believed harmless to tissues.

What is sonar and how does it work

Sound pulse sent underwater; reflects from seabed/object; return time used in depth = 1/2 x v x t.

What is the electromagnetic spectrum

The full range of electromagnetic waves from radio waves to gamma rays ordered by wavelength/frequency.

Relationship between wavelength frequency and energy for EM waves

Longer wavelength = lower frequency = lower energy; shorter wavelength = higher frequency = higher energy.

Key properties of all EM waves

They are transverse and travel at 3×10^8 m/s in a vacuum.

Uses of radio microwaves infrared visible light

Radio: broadcasting; Microwaves: satellite/phones/ovens; Infrared: remotes/thermal imaging/fibres; Visible: vision/photography.

Uses of ultraviolet X-rays gamma rays

UV: security marking/sterilizing water; X-rays: medical imaging/security; Gamma: sterilization/cancer treatment.

Why infrared used in optical fibres

It undergoes total internal reflection efficiently causing low signal loss.

Why microwaves used for satellite communications

They penetrate the atmosphere with low absorption.

Main danger of microwaves

Internal heating of body cells.

Main danger of UV X-rays gamma rays

They are ionizing and can damage DNA leading to cancer.

Why ionising radiation is dangerous

It knocks electrons from atoms and damages DNA.

Why microwaves used for mobile phones and WiFi

They are not strongly absorbed by the atmosphere and can carry high data rates.

Why radio waves used for local radio and Bluetooth

They diffract around obstacles and work well over short distances.

Difference between analogue and digital signals

Analogue varies continuously; digital has discrete values (1/0).

How sound is transmitted digitally

It is sampled then converted analogue to digital to analogue.

Advantages of digital signals

Accurate regeneration; greater range; higher data rate; error checking possible.

What is fluorescence

When substances absorb UV and re-emit visible light.

Why X-rays used for bone scans

They pass through soft tissue but are absorbed by bone.

Protective measures against UV

Sunscreen and UV-absorbing sunglasses.

Mnemonic for EM spectrum order

Raging Martians Invaded Venus Using X-ray Guns.

What is the law of reflection

Angle of incidence = angle of reflection.

How angles are measured in reflection

Angle between ray and normal.

Characteristics of plane mirror image

Virtual upright same size same distance behind mirror.

What is refraction

Change in direction of light crossing a boundary.

When does light bend toward the normal

When moving from less dense to more dense medium.

Does frequency change during refraction

No; only speed and wavelength change.

What is refractive index

A measure of how much a material slows light.

Conditions for total internal reflection

Light from dense to less dense; angle > critical angle.

Uses of total internal reflection

Optical fibres; prisms in binoculars/periscopes.

Principal focus of converging lens

Point where parallel rays meet.

Focal length

Distance from lens center to focus.

Real image

Formed by converging rays; inverted; projectable.

Virtual image

Not formed by real rays; upright; not projectable.

Image when object beyond 2f

Between f and 2f; real; inverted; diminished.

Image when object between f and 2f

Beyond 2f; real; inverted; magnified.

Image when object inside f

Virtual; upright; magnified.

Image from diverging lens

Always virtual upright diminished.

Lens for long-sightedness

Converging lens.

Lens for short-sightedness

Diverging lens.

Dispersion of light

Splitting of white light into colors by refraction.

Color refracted most

Violet.

Visible spectrum colors in order

Red Orange Yellow Green Blue Indigo Violet.

What should you remember when drawing reflection angles?

Angles should be approximately equal; large differences lose marks.

What must you include in a method for investigating refraction?

Equipment list, how to trace rays, how to mark angles, safety precautions.

What do waves transfer and do they transfer matter?

Waves transfer energy without transferring matter.

What is the difference between the motion of wave particles and the wave itself?

The wave moves through the medium, causing particles to oscillate about a fixed point; the particles themselves do not travel with the wave.

What is a wavefront?

A line representing a single wave crest, used to visualize waves from above.

Define amplitude.

The maximum displacement of a wave from its undisturbed position, measured in meters (m).

Define wavelength.

The distance from one point on a wave to the same point on the next wave, measured in meters (m).

Define frequency.

The number of waves passing a point per second, measured in hertz (Hz).

What is a crest and a trough?

A crest is the highest point above the undisturbed position; a trough is the lowest point below it.

What is wave speed?

The speed at which energy is transferred through a medium, measured in m/s.

Write the wave equation and define each variable.

wave speed (m/s) = frequency (Hz) x wavelength (m)

What is the period of a wave?

The time taken for one complete oscillation to pass a fixed point, measured in seconds (s).

How are frequency and period related?

"f = 1/T or T = 1/f"

What is a transverse wave?

A wave where the vibration is perpendicular to the direction of energy transfer.

Give three examples of transverse waves.

Electromagnetic waves, water ripples, seismic S-waves.

What is a longitudinal wave?

A wave where the vibration is parallel to the direction of energy transfer.

Give two examples of longitudinal waves.

Sound waves, seismic P-waves.

What are compressions and rarefactions?

Compressions are where particles are close together; rarefactions are where they are spaced apart.

Can transverse waves travel in a vacuum?

Only electromagnetic transverse waves can; mechanical transverse waves cannot.

Can longitudinal waves travel in a vacuum?

No, they require a medium (solids, liquids, gases).

What is reflection?

When a wave hits a boundary and bounces back into the original medium.

What is refraction?

The change in speed and direction of a wave when it passes from one medium to another.

What changes during refraction?

Speed, wavelength, and direction; frequency remains constant.

What is diffraction?

The spreading out of waves when they pass through a narrow gap or around an edge.

When is diffraction most noticeable?

When the gap size is approximately equal to the wavelength.

What is the normal in wave diagrams?

An imaginary line drawn perpendicular to the boundary between two media.

What is the law of reflection?

The angle of incidence equals the angle of reflection.

How does wave speed change in shallow water?

It decreases.

What happens to wavelength when waves slow down during refraction?

Wavelength decreases.

What happens to wavelength when waves speed up during refraction?

Wavelength increases.

What wave behavior does not change wavelength?

Reflection and diffraction.

Which type of wave has constant pressure and density?

Transverse waves have constant pressure and density.

Which type of wave has varying pressure and density?

Longitudinal waves have varying pressure and density.

How does gap size affect diffraction?

Smaller gaps cause more spreading; larger gaps cause less.

What is the relationship between wave speed depth, and wavelength in water?

In shallow water, speed decreases and wavelength shortens.

What does a wavefront diagram show?

The direction of wave travel, wavelength, and wave shape from above.

What is the unit of frequency?

Hertz (Hz).

What is the symbol for wavelength?

λ (lambda).