04 Waves, Sound And EM Spectrum Flashcards
Transverse wave
Waves that vibrate or oscillate perpendicular to the direction of energy transfer
Electromagnetic waves can move solids liquid and gases in
In a vacuum
What type of wave is a transverse wave
Electromagnetic
Highest point on transverse wave - maximum displacement
Peak or crest
Lowest point on a transverse wave - minimum displacement
Trough
Examples of transverse wave
Vibrations in guitar string
S waves
Electromagnetic waves (e.g. radio,light, x-ray etc)
Longitudinal waves
Waves where the points along its length vibrate parallel to the direction of energy transfer
What does longitudinal waves transfer and not transfer
Transfers energy but not the particles of the medium
What do longitudinal waves move in and cannot move in
Moves in solids/liquids/gases
Cannot move in a vacuum since there’s no particles
Amplitude
Amplitude is the maximum or minimum displacement from the equilibrium
Wavefront
An imaginary surface representing points of a wave that are at the same point in their cycle
Frequency
Number of waves passing a point in a second
- waves with higher frequency transfer has higher amounts of energy
What is frequency measured in
Hertz (Hz)
Wavelength
The distance from one point on a wave to the same point on the next wave
Measured from one peak to another (metres)
Time period
The time taken for a single wave to pass a point
Waves transfer
Energy and information - without transferring matter
Wave speed equation
Frequency x wavelength
Frequency equation
1 / time period
Doppler effect
The apparent change in an observed wavelength and frequency of a wave emitted by a moving source relative to an observer
Describe wavelength of a moving car
Wavelength is larger to an observer behind the moving car
Wavelength is smaller to an observer in front of the moving car
All waves can be
Reflected and refracted
Light is part of a continuous electromagnetic spectrum which includes:
Radio, microwave, infrared, visible, ultraviolet, x-ray, gamma ray
(R M I V U X G)
- all these waves travel at same speed in free space
EM spectrum - long to short wavelength
Radio - microwave - infrared - visible - RV - xray - gamma
EM spectrum - high to low frequency
Gamma - xray - UV - visible - infrared - microwaves - radio
Colours of visible spectrum
Red orange yellow green blue indigo violet
Red has longest wavelength and violet has the shortest
Uses of radio waves
Broadcasting and communications
- used in wireless communication in radios and mobile phone communication
- because they can be reflected from the earths atmosphere
Uses of microwaves
Cooking and satellite transmissions
- at high intensities microwaves are used to heat things in a microwave oven
- because microwaves can penetrate earths atmosphere
Uses of infrared
Heaters and night vision equipment
- emitted by warm objects
- because they can undergo total internal reflection
Uses of visible light
Used in fibre optic communication and photography
- human eye can see
- used for cameras since they can detect visible light
Uses of ultraviolet
Fluorescent lamps
- can also be used to mark things fluorescently such as banknotes
- when some substances are exposed to ultraviolet they absorb it and re-emit them as visible light making them glow (fluorescent)
Uses of xray
- used to observe the internal structure of objects and materials including medical applications
X-rays can pass through most body tissues but are absorbed by denser parts like bones
Uses of gamma rays
Sterilising food and medical equipment
- gamma kills bacteria
Effects of excessive exposure to microwaves
Internal heating of body tissue - damage to internal organs
Effects of excessive exposure to infrared
Skin burns
Effects of excessive exposure to ultraviolet
Damage to surface cells (sunburn) and blindness
Effects of excessive exposure to gamma rays
Kills cells causing cancer and cell mutation
Protective measures against microwaves
Ovens - metal walls and metal grids in the glass door
Protective measures against infrared
Protective clothing like gloves
Protective measures against ultraviolet
Sunglasses to absorb ultraviolet and prevent it from reaching eyes
Sunscreen also absorbs ultraviolet light preventing it from damaging skin
Protective measures against gamma and X-rays
- using minimal levels
- radiographers wear radiation badges to measure the level of radiation exposure
Light waves are what waves
Transverse - can be reflected and refracted
Examples of longitudinal waves
- sound waves
- p-waves
- pressure waves
Reflection
When a wave hits a boundary between two media and does not pass through but instead stays in the original medium
Refraction
A wave passes a boundary between two different transparent media and undergoes a change in direction
Law of reflection
The angle of incidence equals the angle of reflection
Refractive index equation
Sin(i) / sin(r)
Investigating refraction
- place glass block (rectangular Perspex block) on sheet if paper and draw around it
- switch ray box and direct beam light at side of block
- mark on the paper a point where the ray enters the block, point where ray exit blocks, point on exit ray about 5cm away from block
- draw where points are
- draw normal line
- mark angle of incidence and refraction using protractor
- repeat procedure for different angles
Investigating snells law
- draw around glass block on sheet of paper
- draw normal line
- use protractor to measure angles of incidence
- use ray box to direct beam of light
- mark on paper point where ray enters block, point where ray exits block, point on exit ray which is around 5 cm from block - then mark them
- repeat with next angles
Total internal reflection
Angle of incidence is greater than the critical angle
- incident material is denser than second material
When is total internal reflection used
Optical fibres (e.g. endoscopes)
Prisms (e.g. periscopes)
Optical fibres in total internal reflection
Used to reflect light along optical fibres, means they could be used for
- communication, endoscopes (used to see inside patients body), decorative lamps
- light travelling down an optical fibre is totally internally reflected each time it hits the edge of the fibre
Prisms in total internal reflection
Used for periscopes, binoculars, telescopes, cameras
- prisms also were used in safety reflectors for bicycles and cards
Periscopes in total internal reflection
It is a device consisting of two right-angle prisms that can be used to see over tall objects
Critical angle
When the angle of refraction is exactly 90 degrees the light is refracted along the boundary
Critical angle
Sin c = 1 / n
Sound waves are what type of wave
Longitudinal - can be reflected and refracted
Frequency range for human hearing
20 - 20 000 Hz
Investigate speed of sound in air
- use a trundle wheel to measure distance of 100m between 2 people
- one person has 2 wooden block which they bang together above their head to generate sound waves
- second person has a stopwatch which they start when they see person one clap the blocks and stop when they hear the sound
- repeat for various differences
- use equation s=d/t to calculate speed
What equipment can display a sound wave
Oscilloscope and microphone
Investigate frequency of sound using an oscilloscope
- connect 2 microphones to an oscilloscope
- place 2m apart using tape measure
- make a large clap using two wooden blocks next to first microphone
- use oscilloscope to determine time which clap reaches each microphone and the time difference between them
- repeat 5 times and calculate speed of sound by using
- s = 2m / mean time
Oscilloscope
- its a device that can be used to study a rapidly changing signal such as a sound wave/alternating current
Oscilloscope
- its a device that can be used to study a rapidly changing signal such as a sound wave/alternating current
If the frequency of vibration is high
The sound wave has high pitch
If the sound is loud
There’s a large amplitude
When light goes from more optically dense to less dense
Light speeds up
Frequency stays constant
Wavelength increases
Refracts away from normal
When light goes from less optically dense to more optically dense
Light slows down
Frequency stays constant since colour of light doesn’t change
V = f x wavelength
Wavelength decreases
Refracts
When light meets a surface at 90 degrees or 0 degrees to normal
Light goes through
