P5 Flashcards
What happens when waves travel through a medium?
The particles of the medium vibrate and transfer energy between each other.
What is the amplitude of a wave?
The displacement from the rest position to a crest (a peak) or a trough (the lowest point)
What is the wavelength of a wave?
The length of a full cycle of the wave.
What is the frequency of wave?
The number of complete waves or cycles passing a certain point per second. It’s measured in hertz.
What is 1Hz equivalent to in waves?
1Hz = 1 wave per second
What is the period of a wave?
The number of seconds it takes for one full cycle.
How do you calculate the period of a wave?
1 ÷ Frequency
What are the vibrations like in a transverse wave?
They are perpendicular to the direction that the wave travels.
Name examples of transverse waves.
Ripples and waves in water
What are the vibrations like in a longitudinal wave?
They are parallel to the direction that the wave travels.
Name examples of longitudinal waves.
P waves
How do longitudinal waves affect the particles in a medium?
They squash and stretch out the arrangement of particles, making compressions (high pressure, lots of particles) and rarefactions (low pressure, fewer particles)
How can you calculate wave speed, using frequency and wavelength?
Wave speed (m/s) = Frequency (Hz) * Wavelength (m)
How can you measure the speed of sound using two microphones and an oscilloscope?
Measure the distance between the microphones to find one wavelength.
How can you generate waves in a ripple tank?
With a signal generator attached to a dipper. The signal generator moves the dipper up and down to create water waves at a fixed frequency.
How can you measure the frequency in the ripple tank practical?
Frequency = Bobs/Time interval
How can you measure the wavelength in the ripple tank practical?
Wavelength = distance/number of waves
How can you measure the wave speed in the ripple tank practical?
Wave speed = distance travelled/time
What can happen when a wave meets a boundary between two materials?
The wave may reflect
What happens when a wave meets a boundary between two materials and it is absorbed?
The wave is absorbed by the second material, transferring energy to the material’s energy stores.
What happens when a wave meets a boundary between two materials and it is transmitted?
The wave may be transmitted - it arrives on travelling through the new material, often a different speed which can lead to refraction
What happens when a wave meets a boundary between two materials and it is reflected?
This is where the incoming ray is neither absorbed or transmitted, but “sent back” away from the second material.
What is the rule for all reflected waves?
Angle of Incidence = Angle of Reflection
What happens when light rays reflect off smooth surfaces (eg a mirror)?
They reflect all in the same direction, giving a clear reflection.
What happens when light rays reflect off rough surfaces (eg paper)?
They reflect in all different directions. The angle of incidence still equals the angle of reflection, but the rough surface means each ray hits the surface at a different angle.
What is white light?
A mixture of all the different colours of light, which all have a different wave length. All the colours of light in white light are reflected at the same angle.
What is optical density?
How a material affects light
How do different materials affect waves?
Waves travel at different speeds in materials with different optical densities.
How is the frequency of a wave affected when it crosses a boundary between materials?
It stays the same.
Because the frequency remains the same when it crosses a boundary, what happens to the wavelength?
The wavelength changes as the speed changes - it decreases if the wave slows down and increases if it speeds up.
What is refraction?
If a wave hits the boundary between materials at an angle to the normal, this change in speed (and wavelength) makes the wave bend - this is called refraction.
How does speed affect refraction?
If the wave is slower, it will bend towards the normal. If the wave is quicker, it bends away from the normal.
How do electromagnetic waves like light travel in denser materials, and how does this affect their refraction?
They usually are slower in denser materials. So going from air to glass, their wavelength decreases, and they bend towards the normal (if refracted).
What is the order of the wavelengths (longest to shortest)?
Richard Of York Gave Battle In Vein
What is specular reflection?
When waves are reflected in a single direction by a smooth surface. This means you get a clear reflection.
What is scattered reflection?
When waves are reflected by a rough surface and the waves are reflected in all directions. This is because the normal is different for each incident ray.
How can you investigate reflection with a ray box and a mirror?
Trace the incident and reflected light rays - the angle of incidence and angle of reflection will always be equal.
What is the angle of incidence in refraction?
The angle between the incident ray and the normal.
What is the angle of refraction in refraction?
The angle between the refracted ray and the normal.
What happens when white light passes through a triangular prism?
Different wavelengths (colours) of light travel at different speeds in glass, so they refract by different amounts. So when white light passes through a triangular prism, you get a rainbow.
Describe the dispersion of white light triangular prisms
Different colours bend by different amounts again, and on the outside you see a spectrum of colours.
How can you investigate the refraction of light with a ray box, coloured filters and a triangular glass prism?
Repeat using other colour filters - they may refract more or less at each boundary.
What are sound waves?
They are caused by vibrating objects. These vibrations pass through the surrounding medium as a series of compressions and rarefactions.
How do sound waves behave when travelling through a solid?
They are taken through the solid by causing vibrations in the particles of the solid.
How does sound travel in different mediums?
At different speeds. eg. it travels faster in solids than in liquids, and faster in liquids than in gases
What happens to frequency when sound waves travel from one medium to another?
They don’t change.
Because frequency doesn’t change when sound waves travel from one medium to another, what must happen to wavelength?
It changes, as the waves and speed up or slow down. The wavelength increases when sound speeds up, and decreases when sound slows down.
Why can’t sound travel in space?
Sound can’t travel in space because it’s mostly a vacuum (there are no particles to move or vibrate).
What happens to sound waves when they reach your eardrum?
They cause the eardrum to vibrate. These vibrations are passed on to tiny bones in your ear called ossicles, through the semicircular canal and to the cochlea.
What does the cochlea do in the ear?
It turns vibrations into electrical signals which can reach the brain.
How does the brain interpret electrical signals from the cochlea?
It interprets electrical signals as sound of different pitches and volumes, depending on their frequency and intensity.
How does frequency affect the pitch of a sound wave?
A higher frequency sound wave has a higher pitch.
What is human hearing limited by?
The size and shape of our eardrum, and the structure of all the parts within the ear that vibrate to transmit sound. Young people can hear frequencies from about 20 Hz to 20000 Hz.
What is partial reflection?
If a wave is transmitted, some of the wave is usually reflected off the boundary too.
How can you find how far away a boundary is using partial reflection?
If you know the speed of a wave in a medium, you can use the time it takes for the waves to reach a detector and Distance = Speed * Time to find out how far a boundary is.
What is ultrasound?
Sound with frequencies above 20000 Hz, used to see “hidden things”
How does ultra sound work?
They can pass through the body but are partially reflected at boundaries between tissues. If you know the speed of ultrasound in different tissues, you can calculate the distance to different boundaries.
How is ultra sound processed?
The reflections of ultra sound are processed by a computer to form an image. Therefore, ultrasound can be used to form an image of a developing fetus.
Why do you have to divide your answer by two in a reflection question?
The reflection you are given is often the time to travel to a boundary and back, whereas you want to find the distance to JUST the boundary.
What is sonar?
It used by boats and submarines to find out the distance to the seabed or to locate objects in deep water.
Are electromagnetic waves transverse or longitudinal?
Transverse
How do EM waves behave in a vacuum and in different materials?
Different materials - different velocities
What is the range of wavelengths of EM waves?
They range from 10⁻¹⁵m to 10⁴m.
What is the relationship between wavelength and frequency in EM waves?
The longer the wavelength, the lower the frequency. The shorter the wavelength, the higher the frequency.
How are EM waves grouped?
Based on their wavelength and frequency - there are seven basic types.
What is the wavelength of radio waves?
Between 1m and 10⁴m
What is the wavelength of micro waves?
10⁻²m
What is the wavelength of infrared waves?
10⁻⁵m
What is the wavelength of visible light?
10⁻⁷m
What is the wavelength of ultraviolet rays?
10⁻⁸m
What is the wavelength of x-rays?
10⁻¹⁰m
What is the wavelength of gamma rays?
10⁻¹⁵m
What is the relationship between frequency and energy in EM waves?
The higher the frequency, the more energy it transfers.
How do radio waves affect the body?
They are transmitted through the body without being absorbed.
How do microwaves affect the body?
Some wavelengths of microwaves can be absorbed, causing heating of cells, which may be dangerous.
How does infrared and visible light affect the body?
They are mostly reflected or absorbed by the skin, causing some heating too. IR can cause burns if the skin gets too hot.
How do UV rays affect the body?
This damages cells which may cause genetic mutation/cancer/tissue damage/radiation sickness.
How do X-rays and gamma rays affect the body?
They can also pass through skin and be absorbed by deeper tissue.
How are radio waves used?
To transmit information like television and radio shows from one place to another.
What is a general way of looking at EM waves?
They are oscillating electric and magnetic fields.
What does AC cause in electrical circuits?
This EM wave has the same frequency as the current that created it, so it can be a radio wave.
What is oscillation?
Moving back and forth
What do EM waves do to charged particles?
They cause charged particles to oscillate. If the charged particles are in a circuit, this induces an AC of the same frequency as the EM wave that induced it.
How does transmitting information with radio waves work?
If you have a transmitter and receiver, you can encode information in an AC and then transmit it as a radio wave. The wave induces an AC in the receiver.
How are microwaves used?
Communication and cooking
How are microwaves used in communication?
Communication to and from satellites uses microwaves with a wavelength that easily passes through Earth’s atmosphere.
How are microwaves used in cooking?
They penetrate up to a few cm into the food before being absorbed and transferring energy to water molecules in the food, causing the water to heat up. The water then transfer this energy to the rest of the molecules in the food by heating.
What is IR radiation?
Infrared radiation is given off by all objects. The hotter the object, the more it gives off.
How is IR radiation used?
Detecting/monitoring temperature, medical imaging and cooking food
What do optical fibres do?
They carry data over long distances as pulses of light.
How do optical fibres work?
By bouncing light off the sides of a very narrow core. The light enters the core at a certain angle at one end and is reflected again and again until it reaches the other end.
What is fluorescence?
A property of certain chemicals where UV radiation is absorbed and then visible light is emitted.
What can X-rays be used for?
Viewing the internal structure of objects and materials, including our bodies.
How do X-rays work?
They are transmitted by flesh but absorbed by denser material like bone.
How are gamma rays used?
For sterilising things, such as medical instruments, as they can kill microbes.
What is a computerised tomography (CT) scan?
If you use lots of X-rays you can produce high resolution images in 2D and 3D of soft and hard tissues in the body, known as a CT scan.
What are radiotracers?
Radioactive isotopes that patients swallow or are injected with. As they move around the body, they emit gamma rays which can be detected by a gamma camera.
How can doctors see how the body is functioning with tracers?
eg. cancerous tumours use more energy than healthy tissue, so they’ll absorb more of a tracer containing glucose and show up as bright spots
How are infrared cameras used to detect infected or injured areas?
Injured/infected areas are often hotter than other areas, and so produce more IR.
What are the disadvantages of Ultrasound?
The images are fussy and can only be used to make images of soft tissue
What are the disadvantages of X-rays?
They are ionising, so they can damage cells.
What are the disadvantages of Gamma Rays?
They are ionising.
What are the disadvantages of IR imaging?
It doesn’t tell us about much, just temperature.
What are opaque objects?
Objects that do not transmit light. The colour of an opaque object depends on which wavelengths of light are reflected.
How do white objects behave with light?
They reflect all of the wavelengths of visible light equally.
How do black objects behave with light?
They absorb all wavelengths of visible light.
How do transparent/translucent objects behave with light?
They transmit light - not all light hits the surface of the object is absorbed or reflected, some (or most for transparent objects) is transmitted.
What are colour filters?
They are used to filter out different wavelengths of light, so that only certain colour sare transmitted.
What would a red object look like through a blue colour filter?
It would be black. Any of the light reflected by the object is absorbed by the filter.
How do lenses form images?
By refracting light.
What are the two types of lenses?
Convex and concave. They have different shapes and opposite effects on light rays.
How does a concave lens work?
A concave lens caves inwards. It causes parallel rays of light to diverge (spread out).
What is the axis of a lens?
A line passing through the middle of the lens.
What is the principal focus of a concave lens?
The point where rays hitting the lens parallel to the axis appear to come from.
How does a convex lens work?
A convex lens bulges outwards. It causes parallel rays of light to converge (move together).
What is the principal focus of a convex lens?
Where rays hitting the lens parallel to the axis all meet.
What is the focal length of a lens?
The distance from the centre of the lens to the principal focus.
What is a real image?
Where light from an object comes together to form an image on a “screen” eg. the image on the eye’s retina
What is a virtual image?
When light rays diverge (spread out), so the light from the object appears to becoming from a completely different place eg. the image in a mirror
What is the image produced by a concave lens?
Virtual image.
How do you draw a ray diagram for an image through a concave lens?
Where the ray going through the middle of the lens meets the virtual ray is where the top of the image is.
How do you draw a ray diagram for an image through a convex lens?
Where the two rays meet is the top of the image.
How does an object 2 focal lengths from a convex lens behave?
It produces a real, inverted image the same size as the object and at 2 focal lengths on the other side.
How does an object between 1 focal length and 2 focal lengths from a convex lens behave?
It will make a real, inverted image bigger than the object and beyond 2 focal lengths on the other side.
How does an object closer than 1 focal length from a convex lens behave?
It will make a virtual image the right way up, bigger than the object and on the same side of the lens.
What does the convex lens in the eye do?
It focuses incoming light on the retina where it forms an image.
How does the convex lens in the eye behave if the eyeball is too long or the lens is too powerful?
It can’t produce a focused image on the retina. Images of distant objects are brought into focus infront of the retina instead, so the image is blurry.
How do concave lenses correct short-sightedness?
The concave lens diverges light before it enters the eye so that it can be focused on the retina, producing a sharp, clear image.
Why do some people have long sight?
It is when the lens in the eye is too weak or the eyeball is too short. This means that near objects are brought into focus behind the back of the eye, so the image is blurry.
How do convex lenses correct long sight?
It makes light converge before it enters the eye so it can then be focused on the retina.
