Section 4 - Properties Of Waves Flashcards
What is a wave?
Wave transfers energy in the direction of travel
What is the equation for wave speed?
V=f x wavelength
Describe a transverse wave?
A wave that vibrates perpendicular to the direction of travel
What are some examples of transverse waves?
All light and electromagnetic radiation
What is amplitude?
The maximum displacement of a point on a wave from into undisturbed position
What is wavelength?
The distance between the same point on two adjacent waves
What is frequency?
The number of complete waves that pass a certain point per second
Describe a longitudinal wave
A wave that vibrates parallel to the direction of travel
What is an example of a longitudinal wave?
Sound waves
What is wave speed?
Is the speed at which energy is being transferred
What is reflection?
Reflection is when a wave bounces off a surface
What is the law of reflection?
The law of reflection states that the angle of incidence always equals the angle of reflection
How can reflection be shown using water waves
In a ripple tank a dipper will create waves, when a barrier is places the waves will be reflected
What are the two shoes of reflection and explain them
Diffuse - when the light hits a bumpy surface and the image is unclear
Spectral - when the light hits a flat surface and the image is clear
What is refraction?
When waves change direction when passing from one medium to another
Why do waves travel differently in different mediums?
Due to different densities the way will slow down or speed up
What happens when a wave enters a more dense medium?
The wave slows down and bends towards the normal
What happens when a wave enters a less dense medium?
The wave speeds up and bends away from the normal
What happens to wavelength and frequency during refraction.
Wave speed changes and therefore wavelength or frequency must change
Frequency never changes so wavelength must always change
What is dispersion?
Dispersion is when white light spreads out into 7 different colours - a rainbow
This is because he different wavelength inside of visible light refract by different amounts
What is refractive index?
The ratio of the speed of a wave in two different regions
What is the refractive index of a vacuum?
1
What is the equation for refractive index?
Refractive index = speed of light in vacuum / speed of light in material
What is snells law?
It links the equation for refractive index to the angle of incidence and refraction
What is snells equation?
Refractive index = sin(i) / sin(r)
What is total internal reflection?
When no refraction occurs and the light is reflected back into the denser medium
What are the two criteria for total internal reflection?
The rays of light must be going from a more dense to a less dense medium
The angle of incidence must be greater than the critical angle
What is the critical angle?
The angle of incidence when the ray refracts at a 90 degree angle
What id the formula for a critical angle?
SinC = 1/n. Or. Sin critical angle = 1 / refractive index
How do converging lenses work?
Convex lenses that refract the light inwards to a single point
How do diverging lenses work?
In concave lenses the light is refracted outwards and is dispersed
Explain where the principal focus will form.
On convex lenses - where the rays meet
On concave lenses - where the rays image meet behind lens
There is a principal focus on both sides, equal distance from the middle
What is the name of the distance between the principal focus and the centre of the lens?
The focal length - shorter the length the more powerful the lens
What is the difference between a real and virtual image?
A real image is when the light ray come together whereas a virtual image is when they don’t come together where the image appears
How would you describe a real image?
Inverted
Real
Smaller
How would you describe a virtual image?
Virtual
Upright
Smaller
What image will a contact lenses make on a ray diagram?
A virtual image on the same side of the lens as the object
In a convex lens what would happen to the image at different focal lengths?
Over 2F - smaller, inverted, real
At 2F - same size, inverted, real
Over 1F - larger, inverted, real
Under 1F - larger, upright, virtual
What is the order of the electromagnetic spectrum starting with the smallest?
Gamma rays
X rays
Ultra violet
Visible light
Infared
Micro waves
Radio waves
What is used to describe visible light of a single frequency?
Monochromatic
What are some typical uses of radio waves?
Radio and television
What are some typical uses of microwaves?
Mobile phones, microwave ovens
What are some typical uses of infared?
ELectrical grills, thermal imaging, optical fibres
What are some typical uses of visible light?
Photography and vision
What’s re some typical uses of ultraviolet?
Detecting fake items, sterilising water
What are some typical uses to X-rays?
Medical scanning, security scanning
What are some typical uses of gamma rays?
Sterilising food and medical equipment , treating cancer
What is the speed of electromagnetic waves in a vacuum?
3.0 x 10^8 m/s
300,000,000 m/s
What is the difference between sections on the electromagnetic spectrum?
Different wavelength and frequency
In which direction does frequency and wavelength change on the electromagnetic spectrum?
Wavelength decreases from radio to gamma
Frequency increases from radio to gamma
What can be the region of wavelength for a radio wave?
From 1000m to 1m
What can be the region of wavelength for a gamma wave?
1000th of a nano meter
What can be used to see a wave and send it?
A transmitter and a oscilloscope and transmitter
What can be used to receive a radio wave?
A receiver and oscilloscope
What do mobile phones use and why?
Microwaves as they can penetrate through walls and only require a short aerial for transmission
What are the two types of satellites?
Low orbit satellites and geostationary satellites
What are the harmful effects of microwaves?
Internal heating of body cells
What are the harmful effects of infared?
Skin burn
What are the harmful effects of ultra violet?
Damage to skin and eyes leading to skin cancer and eye conditions
What are the harmful effects of X-rays or gamma rays?
Cell mutation or damage
What happens when waves travel through a gap?
It spreads out and diffracts
What is diffraction?
The spreading out of waves as they ‘bend around’ obstacles
What factors effect diffraction?
Wave length and gap size
What happens when gap size and wavelength change in diffraction?
Maximum amount of diffraction when they are equal
Much wider gap is little diffraction
Bit wider gap is diffraction only at edges
Explain how Bluetooth uses electromagnetic radiation.
Uses low energy radio waves to pass through walls
Explain how optical fibres use electromagnetic radiation.
Used for cable television and high speed broadband because visible light can carry high rates of data by interpreting the transmission at the other end. Uses total internal reflection
What is an analogue signal?
They show continuous variation and can take any value within a range
What is a digital signal?
A signal that can only take a certain value
What are the two ways a signal can be transmitted?
As a digital or analogue signal
What are the benefits of digital signalling?
Increased rate if transmission
Increase range of transmission due to more accurate regeneration
What is signal regeneration?
The process of removing noise from a signal when it is received
What is the range of human hearing?
20Hz to 20000Hz
What is the nature of a sound waves?
Longitudinal waves that are caused by vibrating particles
Where does sound travel faster?
In solids, then liquids then gas
What is the speed of a speed of a sound wave in air?
350m/s
How can you determine speed of sound?
Place two microphones a couple metres a way and connect them to a dat logger
Place a sound source on the same line
Measure the distance between the microphones
Find the differnece between time taken to hear sound and divide distance by time
How do changes in amplitude effect a sound wave?
Amplitude increases with loudness
How do changes in frequency effect a sound wave?
Higher the frequency the higher the pitch
What is an echo?
The reflection of a sound wave.
What is an ultrasound wave?
A sound wave with a frequency greater than 20000Hz
What are ultrasound waves used for?
Ultrasound scans on babies as can pass through soft tissue and the echo speed can be interpreted by a computer to make visual image
Used to test materials for flaws
Sonar by using echoes
