P5 Flashcards
What is wave motion described in terms of?
Wavelength, amplitude, frequency, and period.
What is wavelength?
The distance between a point on one wave and the same point on the next, typically in metres.
What is amplitude?
The distance from the equilibrium line to the maximum displacement (crest or trough), in metres.
What is frequency?
The number of waves that pass a single point per second, measured in Hertz (Hz).
What is period?
The time taken for a whole wave to completely pass a single point, measured in seconds.
What is the wave speed formula?
v = f × λ (velocity = frequency × wavelength)
What is the unit of velocity?
M/s
What is the unit of frequency?
Hz
What is the unit of wavelength?
Metres
What happens to velocity if frequency increases?
Velocity increases (directly proportional).
What happens to velocity if wavelength increases?
Velocity increases (directly proportional).
What is the relationship between period and frequency?
They are inversely proportional — smaller period means higher frequency and greater velocity.
What are transverse waves?
Waves with peaks and troughs, and vibrations at right angles to the direction of travel (e.g. light, EM waves).
What are longitudinal waves?
Waves with compressions and rarefactions, and vibrations in the same direction as travel (e.g. sound).
What is a medium in terms of waves?
A substance the wave passes through (e.g. air, water, glass).
What does optical density mean?
It refers to how much a material slows down light, not its physical density.
Does frequency change when a wave enters a new medium?
No — frequency remains constant.
What happens to speed and wavelength in a denser medium?
Both decrease, because frequency stays the same.
Why does colour stay the same in different media?
Because colour depends on frequency, which doesn’t change.
What can happen to a wave at an interface between two materials?
It can be reflected, transmitted, or absorbed.
What determines how a wave behaves at a boundary?
The electrons in the material and the frequency of the wave
What happens when a wave has higher frequency?
It carries more energy — frequency is directly related to energy.
Why do different frequencies interact differently with materials?
Because electrons can only absorb specific energy amounts, depending on frequency.
What causes reflection of a wave?
When a wave hits a flat surface that is opaque and not absorbed.
What is the law of reflection?
Angle of incidence = angle of reflection.
What happens to light on rough surfaces?
It is scattered in all directions — the surface appears matt.
How does reflection happen on a smooth surface?
Light is reflected strongly and in a single direction.
What role do electrons play in reflection?
Electrons absorb light energy and re-emit it as reflected light.
What is transmission of a wave?
When a wave passes through a transparent material.
What affects the amount of transmitted wave?
The transparency of the material — more transparent = more wave passes.
Can transmission include refraction?
Yes — the wave may bend while still passing through.
When does absorption occur?
When the wave’s frequency matches the energy gap of electrons in the material.
What happens to the absorbed energy?
It is not re-emitted immediately, but released over time as heat.
Why do materials appear coloured?
They reflect only that colour of light and absorb the rest.
What is ultrasound?
Sound waves with frequencies above human hearing.
What happens when ultrasound hits a boundary between materials?
It is partially reflected and partially transmitted.
How is distance calculated using ultrasound?
By measuring the time between emission and detection, with a known constant speed.
Why is ultrasound useful for imaging?
It is non-invasive and can detect boundaries under the surface.
Give examples of ultrasound uses.
• Detecting cracks in metal (early reflections)
• Foetus scans in pregnancy
What is sonar?
A use of ultrasound waves on a larger scale.
How does sonar work on ships?
Ultrasound waves are sent underwater, bounce off the seabed, and the time delay gives the depth.
What does the outer ear do?
It collects sound and channels it down the ear canal.
What kind of wave travels down the ear canal?
An air pressure wave.
What happens when sound waves reach the eardrum?
It vibrates at the same frequency as the sound.
What forces act on the eardrum?
• Compression pushes it inward
• Rarefaction pulls it outward
What do the hammer, anvil, and stirrup do?
They vibrate at the same frequency and amplify the sound.
What happens in the cochlea?
Fluid moves, causing small hairs to vibrate.
How does the brain detect sound?
Vibrating hairs trigger electrical impulses in nerve cells.
What makes each hair respond to different frequencies?
Each is sensitive to a specific frequency.
What is the human hearing range?
20 Hz to 20,000 Hz.
Why do we lose high-frequency hearing with age?
Hairs in the cochlea can be damaged by age or loud noise.
Why can’t humans hear ultrasound?
We don’t use sonar — instead, we rely on vision for survival.
What is a ripple tank?
A shallow glass tank filled with water and used to study wave behaviour.
How are waves created in a ripple tank?
A needle or paddle oscillates, producing water waves.
What pattern appears when light shines through the tank?
• Troughs appear light
• Crests appear dark (deeper water scatters more light)
How do you measure frequency in a ripple tank?
Count dark maxima per minute, divide by 60 to get Hz.
How is wavelength measured?
Use a strobe light so waves appear still, then measure distance between two maxima.
How is reflection shown in a ripple tank?
Place an obstruction in the tank.
How is refraction shown in a ripple tank?
Place a thick glass sheet on the floor — water depth decreases and wave speed slows.
Do water particles move with the wave?
No — they move up and down, not along the wave.
How can the fact that water particles don’t move with the wave be shown?
A ping pong ball in the tank doesn’t get carried away.
What does the ping pong ball not getting carried away show about wave motion?
It’s the wave energy that travels, not the water itself.
What type of waves are all electromagnetic waves?
Transverse waves.
Do EM waves require particles to transfer energy?
No — they can travel through a vacuum.
What is the speed of EM waves in a vacuum?
3 × 10⁸ m/s (speed of light).
What happens to frequency when wavelength decreases?
Frequency increases.
What happens to energy when frequency increases?
Energy increases.
Why do higher frequency EM waves carry more energy?
Because energy is directly proportional to frequency.
What are radio waves used for?
Communications
What are microwaves used for?
Cooking — they heat water or fat in food.
What is infrared used for?
Short-range communication and remote controls.
What is visible light used for?
Illumination — lets us see.
What is ultraviolet (UV) used for?
Sterilisation — kills bacteria.
What are X-rays used for?
Seeing through soft tissue and examining bones.
What is gamma radiation used for?
Killing cancer cells in radiotherapy.
Which EM waves are dangerous?
UV, X-rays, and Gamma — they have small wavelengths and high frequency/energy.
Why are high-energy EM waves harmful?
They can mutate cells and cause cancer.
Why do radiotherapists leave the room or wear protection?
To limit exposure to gamma radiation.
Why are pilots at higher cancer risk?
They are exposed to more UV radiation at high altitudes.
How is EM radiation used for imaging the body?
Waves are reflected at material boundaries and detected externally to build images.
What happens with high-energy EM waves in imaging?
They may pass through or be absorbed, rather than reflected.
Where is the detector placed if waves pass through?
On the opposite side of the body from the source.
What causes stronger reflected signals?
Denser materials, because they absorb more wave energy.
What determines how a substance interacts with EM waves?
The wavelength of the EM wave.
What can materials do to EM waves?
Absorb, transmit, refract, or reflect them.
What does glass do to different EM waves?
• Transmits or refracts visible light
• Absorbs UV radiation
• Reflects infrared
Why do different parts of the EM spectrum interact differently?
Due to different wavelengths and frequencies.
What happens when light enters a denser medium?
It slows down.
Which wavelengths slow down more in dense materials?
Shorter wavelengths
What happens to white light passing through a prism?
It is diffracted — different wavelengths refract by different amounts.
What does this diffraction of light cause?
The light spreads out, forming a rainbow.
Why does an object appear a certain colour?
It reflects that specific wavelength and absorbs all others.
What do colour filters do?
They only transmit one wavelength and absorb all the others.
What is the law of reflection?
Angle of incidence = angle of reflection, measured from the normal.
What happens to light entering a denser material?
It bends towards the normal.
What happens to light entering a less dense material?
bends away from the normal.
What are focal points?
Points where light rays converge after passing through a lens.
What happens to rays that pass through the centre of a lens?
They do not change direction.
What shape are concave lenses?
They cave inwards — thinner at the centre than edges.
What do concave lenses do to light?
They spread it outwards (diverge).
How do you draw a ray diagram for a concave lens?
- Draw a horizontal ray from the top of the object to the lens.
- Draw a faint line from the focal point to where the ray hits the lens.
- Extend the ray along this direction — it exits the lens that way.
What are concave lenses used for?
Correcting short-sightedness — light focuses in front of the retina and needs to be spread.
What shape are convex lenses?
They bulge outwards — thicker in the centre.
What do convex lenses do to light?
They focus the light inwards (converge rays).
What are convex lenses used for?
• Magnifying things (e.g. magnifying glasses, binoculars)
• Correcting long-sightedness — light needs to be focused closer
What type of waves are electromagnetic waves?
Transverse waves.
How do electromagnetic waves travel through space?
All EM waves travel at the same velocity in a vacuum (3 × 10⁸ m/s).
How do electromagnetic waves transfer energy?
From the source to the absorber (e.g. sunlight warming skin).
What are examples of EM wave energy transfer?
Infrared cooking food, UV causing skin tanning.
What is the relationship between frequency and wavelength?
They are inversely proportional — higher frequency means shorter wavelength.
How does this apply across the EM spectrum?
Gamma rays have high frequency and short wavelength; radio waves have low frequency and long wavelength.
What are the groupings of the EM spectrum from longest to shortest wavelength? (Low to high frequency)
- Radio
- Microwave
- Infrared
- Visible (red to violet)
- Ultraviolet
- X-rays
- Gamma rays
How do the EM groupings relate to frequency?
They range from low to high frequency as you move from radio to gamma.
What part of the EM spectrum can the human eye detect?
Only the visible light range — a small portion of the full EM spectrum.
How do waves behave differently in solids and liquids for imaging?
• Differences in velocity, absorption, and reflection allow detection of internal structures.
• Example: X-rays absorbed by bone, ultrasound reflected by organs.
What are some imaging techniques using EM waves?
Infrared, X-rays, gamma rays, and ultrasound for medical imaging.
How are radio waves produced?
By oscillations in electrical circuits.
What can radio waves induce?
They can induce oscillations in another electrical circuit.
How can materials interact with EM waves?
They may absorb, transmit, refract, or reflect EM waves.
Does wave interaction depend on wavelength?
Yes — different wavelengths interact differently with the same material.
What causes EM waves to behave differently in different materials?
Differences in the velocity of the wave in those materials.
How does velocity change in denser materials?
The wave usually slows down, which can cause refraction.
What do ray diagrams illustrate? What do ray diagrams illustrate?
Reflection and refraction, and how convex and concave lenses behave.
What is the use of ray diagrams in vision?
They show how lenses correct vision by converging or diverging light rays.
What should ray diagrams for reflection/refraction include?
• Incident ray
• Reflected/refracted ray
• Normal line
• Correct angle relationships (qualitative only)
How is colour linked to wave behaviour?
Colour depends on which wavelengths are absorbed, transmitted, or reflected.
What is specular reflection vs scattering?
• Specular reflection: smooth surface, clear image
• Scattering: rough surface, no clear image
