Waves Flashcards
What is a wave?
An oscillation or vibration passing through a medium
It transfers energy but not matter
How do particles move in a wave?
They oscillate around their rest position, they each push ot pull on their adjacent particles
What are the 2 types of wave?
Transverse and longitudinal
What are transverse waves?
Waves where the oscillations of particles are at right angles to the direction of the energy transfer of the wave
They cannot pass through liquids or gases
What are longitudinal waves?
A wave where the oscillations of the particles are parallel to the direction of the energy transfer of the wave.
This causes areas of compression and rarefaction
What type of waves are sound waves?
Longitudinal
What is wavelength, its symbol and units
The distance between two equivalent points in aadjacent waves. The distance of one complete oscillation
λ
Metres, m
What is displacement?
The distance and direction of a vibrating particke from its rest position
What is amplitude?
The maximum displacement of a vibrating particle
What is a crest of a wave?
The top
What is the trough of a wave?
The bottom
What is the period, its symbol and unit?
The time it takes for one complete oscillation to pass a fixed point
T
seconds, s
What is frequency, its symbol and unit?
The number of complete waves passing a fixed point per second
f
Hertz, Hz
What is the equation that shows the relation between period and frequency?
1
f = –
T
What is the equation for wave velocity?
V = f λ
What is the speed of sound?
340 m/s
How to calculate uncertainty?
½ × range
How to calculate percentage uncertainty?
Mean
What is an echo?
A reflected (sound)wave, which must travel to the boundary and back
REMEMBER TOTAL DISTANCE = 2X REAL DISTANCE
What can happen to a wave when it reaches a boundary?
It can be reflected, absorbed, or transmitted
In which mediums does sound travel faster?
Denser mediums
What happens to a soundwave when it enters a denser medium?
Speed increases, but frequency stays the same so wavelength increases
What is the range of frequencies we can hear called, and what is it?
The auditory range
Between 20Hz and 20,000 Hz
What is an oscilloscope?
An instrument that can be connected to a microphone to visualise sounds. The greater the amplitude of the sound the higher the potential difference induced into the microphone
What is ultrasound?
Soundwaves with a frequency greater than the human auditory range ( > 20,000Hz )
How is ultrasound used to investigate structures, like pregnancy scans?
- incoming ultrasound waves are either transmitted or reflected at each boundary, so each wave travels a different distance (whether reaching baby or not), and the time taken for waves to return to detector can be converted to dustances and an image
What are seismic waves?
Produced by an earthquake, cause surface waves to travel across surface of earth, and body waves which travel through earths core
What are primary waves? (P waves)
Longitudinal, travel faster, come first and travel through solid and liquid
What are secondary waves? (S waves)
Transverse, travel slower, come second and travel through solids only
What is specular reflection?
Reflection of a smooth shiny surface, which sends incoming waves in one direction
What is diffuse reflection?
Reflection off an irregular surface which still follows laws of reflection, but reflect incoming waves in different directions
What is refraction?
The change of direction of a wave when it changes speed.
Occurs at boundary between mediums
What happens when a wave enters a slower medium at an angle?
One edge of wavefront slows down first. The other edge is still travelling quickly, causing the wave to bend towards the normal
What happens when a wave enters a faster medium at an angle?
One edge of wavefront speeds up first. The other edge is still travelling slowly, causing the wave to bend away from the normal
What happens when a wave enters a faster/slower medium along the normal?
Every part of wavefront enters medium at the same time, so continues without changing direction
What do lenses do?
They use refraction to bend light rays to form an image
What does a convex lens do?
Causes light travelling parallel to axis of lens to converge at the principal focus
What is the focal length?
The distance between the lens and the principal focus?
What does a concave lens do?
Causes light to diverge. The principal focus is the point where the rays travelling parallel to the axis appear to come from (they dont its just virtual rays)
What is the symbol for a convex lens?
A vertical line with arrows pointing out at each lens
What is the symbol for a concave lens?
A vertical line with arrows facing inwards at each end
How to draw a ray diagram for a convex lens?
(Eg. From top of a tree)
- ray parallel to axis is refracted such that it passes through principal focus
- ray that travels directly through centre of lens carries on without refraction
How to draw a ray diagram for a concave lens?
(Eg. From the top of a tree)
- ray travelling parallel to axis is refracted so that is continues along the path of a virtual ray from the principal focus before the lens
- ray that passes through middle of lens carries on without refraction
How to describe an image?
- Upright/inverted
- Magnified/diminished
- Real/virtual
How to calculate magnification?
Image height/object height
What are electromagnetic waves?
Transverse waves that can pass through a vacuum (at 3x10⁸bm/s)
Consist of vibrating electric and magnetic fields
Transfer energy from a source until absorbed
Uses of radiowaves?
TVs and radio
Can be reflected off ionosphere and diffracted around curved surface of earth
Uses of microwaves?
Cooking food and satellite communications.
Wavelength is absorbed by water molecules
Uses of infared radiation?
Electrical heaters, cooking food and infared cameras
Uses of visible light?
Fibre-optic communications
Uses of ultraviolet?
Sun tanning and energy efficient lamps
Uses of X-rays and gamma rays?
Medical imaging and treatments
Which electromagnetic waves have greatest wavelength, but also smallest frequency?
Radiowaves
Which electromagnetic waves have smallest wavelength, but also greatest frequency?
Gamma rays
Risks of x-rays and gamma rays?
Cause mutations of DNA, leading to cancer due to ionising radiation
Risks of ultraviolet light?
Can cause skin to age prematurely and increase risk of cancer
How are electromagnetic waves produced?
- electron moves down an energy shell
- within the nucleus
- oscillations in electrical circuits
How does an X-ray work?
X-rays transmit easily through softer tissue, but are absorbed by denser material such as bones, plate detects X-rays and forms an image
What happens when a wave is absorbed by a surface?
The energy of the wave is transferred to the particles in the surface
How does a colour filter work?
They absorb certain wavelengths, and transmit other ones
What colour does an object appear if all wavelengths are reflected equally?
White
What colour does an object appear if all wavelengths are absorbed ?
Black
What colour will a blue object (in white light) appear in red light?
Black, due to there being no blue light for it ro reflect, all incoming wavelengths are absorbed
