Waves Flashcards
(32 cards)
State what a transverse wave is, and give examples
A wave where the vibrations are at 90 degrees to the direction energy is being transferred
E.g. light, waves on string, a slinky spring, or ripples on water
State what a longitudinal wave is, and give examples
A wave where the vibrations are along the same direction energy is being transferred
E.g. sound, shockwaves, or a slinky spring
Describe what a wavefront is
Imaginary planes that cut across all waves, connect the points on adjacent waves which are vibrating together
Describe the Doppler effect
The apparent change in wavelength due to relative motion between the source and the observer
The frequency of a wave from a source moving towards you will be higher and its wavelength will be shorter than the wave produced by the source
Wave speed is constant, so if the source is moving, it will catch up to the waves in front of it, causing the wavefronts to bunch up in front of the source and spread out behind
What is the order of the EM waves in order of decreasing wavelength
Radio waves
Microwaves
Infrared radiation
Visible light
Ultra violet
X-rays
Gamma rays
What is a use of radio waves
Used for communications
Long waves are bent around the Earth
Short waves are reflected off the ionosphere to FM radio and TV
What is a use of microwaves
Used for satellite communication, a signal from a transmitter is transmitted into space, it is received by a receiver dish which transmits the signal back disk where it is received by a satellite dish on the ground
They are used for heating food as well, the food molecules absorb the microwaves which penetrate a few cm into the food before being absorbed
What is a use of infrared radiation
Heating e.g. grills or cooking food
Monitoring temperature
Night-vision allows objects to be detected in the dark using infrared radiation, the equipment turns the detection into an electrical signal which is displayed on a screen as a picture
Describe how optical fibres are used
Waves (pulses of light) are rebounded of very narrow cores and are reflected again and again until they reach the other end of the fibre
They are often used for telephone and broadband internet cables as well as sometime being used for medical purposes
How is visible light used for photography
Cameras use a lens to focus visible light onto a light-sensitive film or sensor
The lens aperture controls how much light enters the camera
The shutter speed determines how long the film is exposed to light
Photographers can capture as little or as much light as they want in their photograph
How is ultraviolet used in fluorescent lamps
Ultraviolet waves are absorbed, and visible light is emitted
Phosphor coating emits the visible light
They are more energy-efficient than filament light bulbs
How do x-rays work
X-rays are directed through a detector plate
Radiographers use x-rays to help doctors diagnose broken bones
X-rays pass through flesh but not through denser materials like bones or metal
X-rays can lead to mutations which can lead to cancer so lead aprons and shields are used as well as minimising x-ray radiation exposure
Lighter parts of an x-ray image are areas where fewer x-rays get through
How is gamma radiation used for sterilisation
Kill all the microbes in medical equipment without damaging them due to high temperatures
They kill microbes in food, allowing longer lifespans without having to freeze or cook it, or preserve it using any other methods
How can EM waves be harmful to humans
Passes through soft tissue without being absorbed
Can cause heating of the cells
Can cause cancerous changes in living cells
What are the dangers of microwaves and how are they avoided
The waves have similar frequencies to o the vibrations of many molecules
Internal heating of molecules in living things occurs, microwaves heat human body tissue in this way
Ovens have shielding to prevent microwaves from reaching the user
What are the dangers of infrared radiation and how can they be avoided
High frequency causes heating effect, it can cause skin burns
Using insulating materials prevents IR from reaching and damaging your skin
What are the dangers of ultraviolet waves and how are they avoided
Can cause damage to surface cells as well as cause blindness
Some UV can be ionising, causing mutation or destruction, and cancer
Sunscreen with UV filters reduces risk as well as staying out of strong sunlight
What are the dangers of Gamma waves and how can they be avoided
Very ionising and can penetrate through the body
Can cause cell mutation or destruction, leading to tissue damage or cancer
Lead lined boxes should be used to store gamma ray sources
Limit time under exposure to gamma rays
Explain how waves can be refracted
Waves travel at different speeds in substances which have different densities
If a wave goes from a less dense medium to a more dense medium but hits the boundary straight on, it will slow down but maintain the same direction
If it hits the more dense medium boundary at an angle, the part that hits the wave slows down, while the the other part carries on at the faster speed, causing a change in direction
Describe a practical showing that rays passing through a glass block are refracted twice
Shine a light through a rectangular glass block that has been placed on top of a piece of paper
Trace the incident and emergent rays onto the paper and draw the refracted ray by connecting the ends of the two other rays
The light direction emerging from the other side of the block should be the same as the light direction it was travelling in to begin with
What type of light do triangular prisms disperse
White light is dispersed into different colours as it enters the prism and the different wavelengths are refracted by different amounts
Rainbow effect
Violet is bent the most
How can you find the refractive index of glass using a glass block
Draw around a rectangular glass block on a piece of paper and direct a ray of light through it at an angle
Trace incident and emergent rays followed by the refracted ray
Draw a normal at 90 degrees to the edge of the block, at the point where light enters
Use a protractor to measure angle if incidence and angle of refraction
Describe an investigation you can do to show total internal reflection
Mark the positions of the rays and gather block on paper and use a protractor to measure angle i and angle r
If the angle of incidence is less than critical angle go then only a little bit of light is internally reflected
If the angle of incidence is equal to the critical angle then there is a lot of internal reflection
If the angle of incidence is greater than the angle of reflection then total internal reflection has occurred
What is total internal reflection
When no light leaves the medium
