2. Waves Flashcards
What do waves do?
They transfer energy and information without transferring matter
What are transverse waves?
Waves that oscillate perpendicular to the direction of energy transfer
What are longitudinal waves?
Waves that oscillate parallel to the direction of energy transfer
They show areas of compression and rarefraction
What kind of waves are electromagnetic waves?
Transverse
What kind of waves are sound waves?
Longitudinal
What kind of waves are mechanical waves?
They can be either Transverse or Longitudinal
What is a wavelength?
The distance between the same point (i.e. the crest) on successive waves
What is the amplitude?
The distance between the maximum point of oscillation and the line of equilibrium
What is frequency?
The number of wave cycles per time unit
What happens when identical sets of waves overlap?
They interfere
What is Constructive interference?
When waves arrive in sync and so therefor add to each other
What is destructive interference?
When waves arrive half a wavelength out of sync and cancel each other out
Reflection
When waves are reflected, the angle of incidence = angle of reflection
What is a ‘Normal” line?
A line constructed perpendicular to the reflecting/refracting surface at the point of incidence
What is refraction?
When light waves undergo a change in direction as they from one medium to another at an interface
What can refraction by a prism lead to?
Dispersion
What is meant by time period?
The time it takes for one complete waves length to pass through a point
As frequency increase, the time period decreases
Frequency = 1 / Period
Frequency (Hz) = 1 / Time period
v = f × λ
Speed (m/s) = frequency (Hz) x Wavelength (m)
What happens when light enters a more dense medium?
It is refracted towards the normal
What happens when light enters a less dense medium?
It is refracted away from the normal
Why are waves refracted?
Due to change of speed
How is refractive index defined?
Speed of light in vacuum (air) /
Speed of light through the medium
n = sin i / sin r
Refractive index = sin(angle of incidence) / sin(angle of reflection)
What is Total internal reflection?
A special case of refraction, when the angle of incidence within the more dense medium is greater than the critical angle, meaning the light is reflected within the more dense medium
What is the critical angle?
The angle at which the refraction takes the light wave along the interface
n = 1 / sin c
Refractive index = 1 / sin (critical angle)
How is sound detected?
Sound waves are longitudinal waves, and cause vibrations in a medium, which are detected as sound
What is the range of human hearing?
20 Hz - 20 000Hz
What do we call sound waves with frequencies greater that that of human hearing?
Ultrasound
What determines a sounds pitch?
Frequency
What determines a sounds volume?
Amplitude
How is Ultrasound used to calculate how far away a boundary is?
Fired at a boundary, and partially reflects reaching the detector the time this takes is used to calculate the distance
Uses of Ultrasound?
Pre-natal scanning
Removal of kidney stones
What is an echo?
A reflected sound wave
What is an electromagnetic wave?
A wave that can travel through vacuums
Created by the vibration of an electric charge
What is the range in wavelengths of the electromagnetic spectrum?
from 10^-15m to 10^4m
What is the link between the wavelength, and the frequency and energy?
The shorter the wave length the higher the frequency and energy
Properties of X-rays:
Affect photographic film in the same way as light
They are absorbed by metal and bone
Transmitted by soft tissue
Order of the EM spectrum in order of increasing energy and frequency
Radio Waves Microwaves Infrared Visible light Ultraviolet X-rays Gamma rays
Uses of:
Radio waves
Television and radio
Bluetooth
Uses & harms of:
Microwaves
Uses : Mobile phones and satellite televisions
Harms : Heating of body tissue
Uses & harms of:
Infrared
Uses: remote controls
Harms: skin burns
Uses:
Visible light
Uses : Photography
Uses & harms of:
Ultraviolet
Uses: security marking
Harms: Skin cancer and blindness
Uses & harms of:
X-rays
Uses: Medical imaging
Harms: High doses kill cells
Uses & harms of:
Gamma rays
Uses: Sterilising surgical equipment and killing harmful bacteria in food
Harms: Genetic mutations
What precautions can be taken to minimise the levels of radiation that people who work with it are exposed to?
wearing protective clothing
keeping as far away as is practicable - for example, by using tongs
keeping your exposure time as short as possible, and
keeping radioactive materials in lead-lined containers, labelled with the appropriate hazard symbol
Doppler effect:
If a wave source is moving relative to an observer there will be a change in the observed wavelength and frequency
When the source is moving away, wavelength increases and the frequency decreases
When the source is moving closer, the wavelength decreases and the frequency increases
What happens to light when, the light waves are stretched?
They move closer to the red end of the spectrum
This is called RED SHIFT
What are the furtherest galaxies from us doing?
Moving away from us the quickest so they appear the most red
What does Red shift provide evidence for?
The expansion of the Universe and therefore the Big Bang Theory (that the universe began from a very small initial point)
What is CMBR?
Cosmic microwave background radiation is a form of electromagnetic radiation that was present shortly after the beginning of the Universe
Big Bang theory is the only theory that fits with CMBR
How do lenses form an image?
By refracting light, bringing it to a focus at the principle focus
What is focal length?
The distance from the lens to the principal focus
What is the focal length determined by?
The refractive index of material from which the lens is made
The curvature of the two surfaces of the lens
What is another name for a convex lens?
A converging lens
What is another name for a concave lens?
A diverging lens
What structures does the eye contain?
Retina Lens Cornea Pupil / Iris Ciliary muscle suspensory ligaments
What does the retina do?
The retina is the light-sensitive layer at the back of the eye that contains rods and cones that convert incident light energy into signals
What does the cornea do?
Acts as slight protection and first refractive layer, for light as it enters the eye
What does the lens do?
Focus light onto the retina
What does the ciliary muscle do?
It changes the shape of the lens to focus light on the retina
It is attached to the suspensory ligaments which are attached to the lens
What does the pupil do?
Allows light into the eye
What does the iris do?
Controls how much light enters the pupil
Long sightedness
Caused by the eyeball being too short
Focus point being behind the back of the eyeball
Or the lens not being able to focus
Can be counteracted by a converging lens
Short sightedness
Caused by the eyeball being too long
Focus point is before the retina
Or the lens not being able to focus
Can be counteracted by diverging lens
What are lasers?
Concentrated sources of light
Can be used for:
Cutting, Cauterising, burning and also laser eye corrections
Evaluate the structure of a camera compared to an eye:
In an eye the image is brought to focus on the retina by a changing shape of the lens
In a camera the image is brought to focus on the film by by varying the distance between the film and the lens
The film in the camera is equivalent to the retina in the eye
Magnification = ?
Magnification = image height / object height
1/u + 1/v = 1/f
1 / object distance + 1 / image distance = 1 / focal length
