3 Waves Flashcards
Waves
Oscillations in a medium that transfer energy not matter. Examples are water waves, electromagnetic waves and sound waves.
What do waves consist off
The ripples are made up of a series of peaks (high points) and troughs (low points) moving outwards from the source of a disturbance
Wavelength
The wavelength is the distance between any two similar points in a wave pattern such as two adjacent crests. The wavelength can also be measured between two adjacent troughs.
Amplitude
The amplitude of the wave is a measure of the energy it carries. For a transverse wave the amplitude is the height of the wave above the central position.
Frequency
Number of waves produced in each second. Measured in HERTZ(Hz)
Period(time)
Time taken for one whole wave to pass a period in space
The wave formula
v=fλ
wave speed = frequency × wavelength
Transverse Wave
Particles at right angles to the wave’s direction of travel(Propagation)
S waves
Longitudinal waves
Particles parallel to the waves direction of travel
P waves
Law of reflection for plane mirrors
The angle of incidence is equal to the angle of the reflection
The three most important behaviours of waves are:
reflection: a wave ‘bounces’ off a boundary
refraction: a wave moves from one medium to another
diffraction: a wave spreads as it moves through a gap.
Incident wave
The path of a wave which travels from the source.
Reflected wave
The path of a wave which has reflected from a surface.
Refraction
Refraction is the bending of light as it travels between 2 different mediums with different refractive index ( the higher the stronger)
Refractive index
n = Sin I ÷ Sin R
Diffraction of waves
When a wave passes through a gap, the wave spreads outwards from the gap. This effect is called diffraction.
Changes in refractive index
Low to High: Bend towards normal
High to Low: Bend away from normal
Normal
A line drawn perpendicular to a surface from which angles of incidence, reflection and refraction are measured.
Angle of Incidence
The angle at which a wave or ray approaches a boundary or surface. Measured from the normal.
Angle of reflection
The angle at which a wave or ray leaves a boundary or surface after being reflected. Measured from the normal.
Virtual image
An image formed by a lens which cannot be projected onto a screen as the rays of light only appear to pass through it. Virtual images are formed by mirrors and some lenses.
Real image
An image formed by a lens which can be projected onto a screen. Rays of light pass through the points on a real image.
Formation of an image in a plane mirror
An image is formed when all the rays from one point on the object are reflected by the mirror, and then seem to come from a single point behind the surface of the mirror.
Refraction of a light ray will cause it to change direction towards or away from a normal
When light moves from air into glass, the light will slow down. This causes it to change direction towards the normal.
When light moves from a glass block into air, then it will speed up. This causes a change in direction away from the normal.
If the ray enters or leaves the block normal to the surface, then there is a change of speed, but the ray continues to travel in the same direction.
Internal reflection
When light moves across a boundary between materials some of it is reflected back from the boundary.
Total internal reflection
When light is perfectly reflected as its reaches a boundary. The effect only happens if the angle of incidence is above the critical angle.
Critical angle
The largest angle of incidence which allows light to leave a material. Above this angle the light will be totally internally reflected.
critical angle
Refractive index
n=1/sin c
C= critical angle
Optical fibres
Total internal reflection is a very useful effect, as it allows us to direct light to travel in any path we want. This effect is used in optical fibres. These are very thin glass or plastic tubes which can bend.
Converging lens
A lens which converges (brings together) rays of light.
Diverging lens
A lens which diverges (spreads out) rays of light.
Focal length
The distance between the centre of a lens and it’s principal focal. Measures along the principal axis.
Enlarged
An image formed by a lens that is larger than the object.
Upright
An mage formed by a lens that is the same way up as the object.
Inverted
An image is formed by a lens which is upside down compared to the object.
Cornea
A tough, colourless and transparent outer layer covering the iris and pupil of the eye. Most refraction of light happens through the cornea.
The lens of the eye
This is a converging lens made from a tough, transparent material. Tiny muscles which surround it can be used to stretch it to make it thinner. This increases its focal length and allows us to focus on objects which are further away.
Short-sightedness
Over time, the lens in your eye may become difficult to stretch and so it cannot be made thin enough by the eye muscles. This results in a condition known as short-sightedness. The thick lens causes light for distance objects to be focused in front of the retina so we cannot see them clearly. The far point of the eye is no longer at infinity and may only be a few metres away.
Long-sightedness
Some people develop long-sightedness. This is a condition where the lens cannot be made thick enough, or the eyeball is too short. The result is that the light from nearby objects is focused on a point behind the retina giving a blurred image. The near point becomes further away from the eye, meaning that you might have to hold writing further away to read it easily.
Dispertion
he separation of white light into its constituent colours due to the differ speeds of different wavelengths of light passing through a material.
Visible light
Electromagnetic waves with a wavelength that we can see.
Infrared
Electromagnetic waves used for cooking (grilling) and in optical fibres for communications. Emitted by all objects but more radiation is emitted by hotter objects.
Ultraviolet
Electromagnetic waves emitted from very hot objects like the Sun. Can cause sunburn, skin cancer and damage eyes.
Radio waves
A type of transverse wave that consists of vibrating electric and magnetic fields. Electromagnetic radiation does not need a medium to travel through and travels at the highest speed possible in a vacuum.
The rule with waves and vacuums
All electromagnetic waves travel at the same speed in a vacuum – at 3.0×108 m/s (300000000 m/s)
. This is the fastest speed anything can possibly travel – fast enough for an electromagnetic wave to travel around the circumference of the Earth seven and a half times in one second.
Microwaves
Electromagnetic waves with a wavelength of a few cm or mm. Used for cooking and communication technology.
X-rays
High energy electromagnetic waves which can pass through some materials but not others. Used to take pictures of bones, teeth for example. Can be harmful.
Gamma rays
Electromagnetic waves are emitted by radioactive materials.
Use of Radio waves
Communication (Radio and TV), RFID tags
Use of Microwaves
Heating food, Cell phone signals, Satelites
Use of IR
Heating, Remote control, Alarms, Thermal imaging
Use of Visible Light
Sight, photography/ film, Illumination
Use of UV
Sterilisation, forgeing detection
Use of X-rays
Medical imaging, security scanner
Use of Gamma rays
Quality control, Imaging, cancer treatments, food sterilisation
Dangers of Microwaves
Heating of cells
Dangers of Infrared
Skin burns
Dangers of X-rays and Gamma rays
Overexposure can cause DNA damage–> Mutilation(general damage)
Dangers of UV
Damage to cells, DNA, Eyes –> cancer or eyesight degradation
Anauloge
A continuous signal that can have any value and be increased or decreased by infinitely small divisions.
Digital
A signal that has a set of discrete values, normally 0 or 1.
Regeneration
A way of removing noise from a digital signal so it can be transmitted further.
Medium
The material through which a wave passes. The plural of medium is ‘media’. Waves travel at different speeds in different media.
Pitch
How we perceive the frequency of a sound wave. When a sound wave has a high frequency (for example 1000 Hz), we hear it as a high-pitched sound; when the frequency is low (e.g. 20 Hz), we hear a low-pitched sound.
Sound
When an object, like the string of a guitar vibrates, it produces a sound wave which travels through the air. The wave travels from the source (the guitar string) through a medium (the air) and reaches a detector (our ear). The wave then causes our ear drum to vibrate, and this vibration passes through a series of tiny bones into our inner ear, stimulating nerve cells to send electrical signals to our brain. These signals cause the sensation of sound.
The properties of the sound wave can vary depending on how the object producing the sound is vibrating.
If the vibrations are made larger, by plucking the string harder, then the amplitude of the sound wave will become greater. Increasing the amplitude increases the energy transfer and so the sound will be louder.
If the object is made to vibrate back and forth more times each second, then it produces vibrations at a higher frequency. The pitch of the sound we hear will be higher.
Changing the properties of a sound wave.
Change to the source of vibration What happens to the sound wave? What happens to what we hear?
faster vibrations increased frequency increased pitch
larger vibrations increased amplitude increased loudness
How sound waves travel
Sound waves are a type of longitudinal wave. The particles which form the wave move back and forth in the same direction as the wave travels. As the wave passes through the air, it produces regions where the air particles are compressed closer together, known as compressions , and regions where the air particles are spread out slightly further than normal, known as rarefactions
Compressions
A region of air (or another material) where the particles are closer together than normal due to a sound wave passing through it.
Refractions
A region of air (or another material) where the particles are further apart than normal due to a sound wave passing through it.
Reflection of sound waves
Sound waves can reflect when they reach a boundary between materials. This happens when a sound wave moving through the air reaches a hard surface, such as a wall. The wave hits the wall and is reflected away from the wall, back towards its source. The reflected sound wave is called an echo.
The speed of sound in different media
Sound waves travel at different speeds in different materials. Many factors affect this speed, including the density and elasticity of the materials. In general, however, sound travels slowest in gases, faster in liquids and fastest of all in solids.
How to measure the speed of sound
A better approach to measuring the speed of sound is to use an electronic system to start and stop the stopwatch. This eliminates timing errors and gives a more accurate measurement of the speed of sound.
what happens if there is no medium for sound to travel
Sound waves can only travel through a medium made up of particles, they cannot exist where there are no particles. A vacuum is completely empty space and so sound waves cannot pass through it at all. This means that sound does not travel through empty space.
Ultrasound
Sound waves with a frequency above 20 000 Hz. Humans cannot hear sound waves above this frequency.
Uses of ultrasound
Using ultrasound to measure distances
Sonar
Using ultrasound to analyse materials for damage
Using ultrasound in medical scanning
Monochromatic
is light of a single frequency
Speed of light
3 × 10^8 (m / s)
Speed of sound
Air= 343m/s
Water= 1500m/s
Refractive index
speed of light in vacuum ÷ Speed of light in a medium
Wavelength of the electromagnetic spectrum from high to low
Frequency of the electromagnetic spectrum from low to high
Radio
Microwave
Infrared
Visible light
Ultra-violet
X-rays
Gamma rays
Sound wave:
Compression
Refraction
(region where) particles are close(r) together (than normal) OR (region where) there is a great(er) pressure (than normal)
(region where) particles are further / far apart (than normal) OR (region where) there is a low(er) pressure (than normal)
Wavelength and frequncey
wave length ^-!
Radio
Micro
Infrared
Visible
Ultraviolet
Xrays
Gamma
