Waves Flashcards
what is a transverse wave?
The oscillations are perpendicular to the direction of energy transfer.
A spring wiggled side to side gives a transverse wave
What is a longitudinal wave?
The oscillations are parallel to the direction of energy transfer.
If you push the end of a spring, you get a longitudinal wave.
Examples of transverse waves?
-all electromagnetic waves
-ripples and waves in water
- wave on a string
{most waves}
Examples of longitudinal waves?
- sound waves in air, ultrasound
- shock waves, seismic waves
How do you calculate the wave speed?
Wave speed (m/s) = frequency (Hz) X wavelength (m)
What is the frequency of a wave?
The number of complete waves passing a certain point per second. Measured in hertz (Hz)
What is the amplitude of a wave?
The maximum displacement of a point on the wave from its undisturbed position.
What is the wavelength?
The distance between the same point on two adjacent waves
How do you calculate the period of a wave?
The amount of time it takes for a full cycle of waves to pass a point
Period = 1/ frequency
What is the angle of incidence?
Angle of incidence = angle of reflection
-the angle between the incoming wave and the normal
What is specular reflection?
When a wave is reflected in a single direction by a smooth surface (eg when lit is reflected by a mirror you get a clear reflection)
What is diffuse reflection?
When a wave is reflected by a rough surface (eg paper) and the reflected rays are scattered in many different directions
What is refraction?
When a wave crosses a boundary between materials at an angle, it changes direction and so it is refracted
What is the frequency of a wave?
The number of complete waves passing a certain point per second. Measured in hertz (Hz)
What is the amplitude of a wave?
The maximum displacement of a point on the wave from its undisturbed position.
What is the wavelength?
The distance between the same point on two adjacent waves
How do you calculate the period of a wave?
The amount of time it takes for a full cycle of waves to pass a point
Period = 1/ frequency
What is the angle of incidence?
Angle of incidence = angle of reflection
-the angle between the incoming wave and the normal
What is specular reflection?
When a wave is reflected in a single direction by a smooth surface (eg when lit is reflected by a mirror you get a clear reflection)
What is diffuse reflection?
When a wave is reflected by a rough surface (eg paper) and the reflected rays are scattered in many different directions
What is refraction?
When a wave crosses a boundary between materials at an angle, it changes direction and so it is refracted
Which rule applies to all reflections?
Angle of incidence = angle of reflection
What is an experiment you could do to investigate refraction?
- place rectangular transparent block on a piece of paper and trace around it
- use a ray box or laser to shine a ray of light at the middle of one side of block
- trace the incident Ray and mark where light Ray emerges on the other side of block
- remove block and join up incident Ray and emerging point to show the refracted Ray brought the block
Why must you do light experiments in a dim room?
- so you can clearly see the paths of the rays of light
- Ray box and laser means more accurate angle measurements as Ray’s can be traced more accurately
What is an experiment to investigate reflection and light?
- take piece of paper and draw a straight line across it. Place an object on the line
- shine a ray of light at the objects surface and trace the incoming and reflected light beams
- draw the normal at the point where the Ray hits the object
- use protractor to measure angle of incidence and angle of reflection
- repeat for a range of objects
What is an electromagnetic wave?
- transverse waves that transfer energy from a source to an absorber
- they all travel at same speed through air or a vacuum (space)
- they form a continuous spectrum over a wide range of frequencies
- grouped into seven basic types depending on their wavelength and frequency
How are radio waves created?
- using an alternating current in an electrical circuit
- object in which charges (electrons) oscillate to create the radio waves is called a transmitter
What are uses of EM waves?
Long radio waves- can be transmitted from around the world even if the receiver isn’t in sight of the transmitter
Short wave radio waves-can be received at long distances from the transmitter
Bluetooth-uses short wave radio waves
TV/radio- very short wavelengths and you must be in sight of transmitter
What is infrared radiation?
Given out by all objects and the hotter the object, the more IR radiation it gives out
What do infrared cameras do?
- used to detect infrared radiation and monitor temperature
- it detects IR radiation and turns it into an electrical signal which is displayed as a picture on a screen
- the hotter an object is, the brighter it appears
What is an optical fibre?
Thin glass or plastic fibres that carry data over long distances as pulses of visible light
- work because of reflection
- light is not easily absorbed or scattered as it travels along a fibre
What is ultraviolet radiation?
Produced by the son and exposure to it is what gives people a sun tan.
-present in sun beds in UV lamps to give artificial tan > overexposure can be dangerous
What is the purpose of X Ray’s?
- To identify any broken bones in the body
- can treat people with cancers (radiotherapy)
How do X rays work?
It is the amount of radiation that is absorbed that gives you an X Ray image
-the brightest bits are where fewer X Ray’s get through so they aren’t as accurate as the darker parts
How are X Ray’s and gamma rays used in radiotherapy?
-high doses of these Ray’s kills all living cells so they are directed to kill the cancer cells in a specific area
What are the dangers of X rays and gamma rays?
- types of ionising radiation which can causes gene mutation or cell destruction and cancer
- radiographer swear lead aprons and stand behind a lead screen because it doesn’t emit this radiation
How are TV signals transmitted from a transmitter on the ground to a house?
- transmitted through atmosphere into space
- picked up by satellite receiver orbiting Earth
- satellite transmits signal back to Earth in a different direction
- then received by a satellite dish connected to the house
How do lenses form images?
They refract light and change its direction
What is a convex lens?
- bulges outwards
- causes rays of light parallel to the axis to be brought together at the principal focus
What is a concave lens?
- caves inwards
- causes rays of light parallel to axis to spread out (diverge)
- ALWAYS produces a virtual image that is upright and smaller than the object
What is a real image?
Where the light from an object comes together to form an image on a screen
What is a virtual image?
When the rays are spreading out so the light from the object appears to be coming from a completely different place
Eg your face in a mirror and looking through a magnifying glass
How do you describe an image properly?
- how big it is compared to object
- whether it’s upright or inverted (upside down)
- whether it’s real or virtual
How do you calculate the magnification?
Magnification = image height / object height
What are opaque objects?
They do not transmit light. When visible waves hit them, they absorb some wavelengths of light and reflect others
What are transparent/translucent objects?
They transmit light. Not all light that hits the surface of the object is absorbed or reflected-some can pass through
What are colour filters used for?
To filter out different wavelengths of light so that only certain colours are transmitted, the rest are absorbed
Eg red cellophane (red or black)-transparent object
What is a perfect black body?
An object that absorbs all of the radiation that hits it. No radiation is reflected or transmitted
-the best possible emitters of radiation
What does the temperature of the earth depend on?
The amount of IR radiation it reflects, absorbs and emits
Why does the temperature of the earth stay fairly constant?
- during day lots of radiation (light) is transferred to Earth from sun and is absorbed-increase in local temp
- at night less radiation is being absorbed than it is being emitted-decrease in local temp
- overall temp of earth stays fairly constant
What causes a sound wave?
- vibrating objects.
- vibrations passed through the surrounding medium as a series of compressions and rarefactions
Why does a sound wave travel best in a solid and not in a gas, liquid or space?
- when a sound travels through a solid, it causes the particles to vibrate
- sound can’t travel in space because it’s a vacuum (no particles to vibrate)
How do sound waves travel to the ear?
- vibrations passed to ossicles in ear, through semicircular canals and to the cochlea.
- cochlea turns thee vibrations into electrical signals which are sent to the brain and so we hear the sound
What range of sound can humans hear? What affects this?
20Hz-20kHz
-hearing is limited by size and shape of our ear drum
What are echoes? How are they caused?
- sound waves are reflected by hard flat surfaces
- echoes are just reflected sound waves
What is an ultra sound?
- electrical device which produce electrical oscillations of any frequency
- converted into mechanical vibrations to produce sound waves beyond range of human hearing
How do microphones work?
Sound waves cause diaphragm to vibrate and this movement is transferred into an electrical signal
How are ultrasounds used in the medical industry?
- ultrasound waves can pass through body
- when they reach boundary between two different media (eg fluid and skin of foetus) some of the wave is reflected back and detected
- the exact timing and distribution of these echoes are processed by a computer to produce a video image of foetus (scan)
What happens when there is an earth quake?
Seismic waves are created and travel through the earth. They are detected by seismometers
What happens when seismic waves reach a boundary?
When they reach a boundary between different layers of material inside the earth, some waves will be absorbed and some will be refracted
What usually happens if waves are refracted?
They change speed gradually, resulting in a curved path. But if properties change suddenly, the wave speed changes abruptly and the path has a kink
What are P-waves?
-longitudinal
-travel through solids and liquids
-travel faster than S-waves
(Seismic wave)
What are S-waves?
-transverse
-can’t travel through liquids or gases
-slower than P-waves
(Seismic wave)
