Waves Flashcards
Define wave
Vibrations that transfer energy.
What are transverse waves?
Waves where wave motion vibrates perpendicular to the direction of energy transfer.
What are the properties of transverse waves?
-Energy transfer and wave motion are perpendicular
-Transfer energy, not particles
-Move in solids and on surfaces of liquids (only some in liquids, gases and vacuums
-Constant velocity+ density
What are examples of transverse waves?
light, S-waves (seismic), EM waves
What are longitudinal waves?
Waves where wave motion vibrates parallel to energy transfer
What are the properties of longitudinal waves?
-Energy transfer and wave motion are parallel
-Transfers energy, not particles
- Can move in liquids, solids and gases (not vacuums)
- Changing density+ pressure
What is it called when particles are close together in longitudinal waves?
Compression
What is it called when particles are far apart in longitudinal waves?
Rarefaction
What are examples of longitudinal waves?
Sound waves, P-waves and pressure waves
What does a wave front diagram show?
Waves viewed from above
What is amplitude?
Distance from undisturbed position to the peak or trough (metres)
What is wavelength?
Distance from one point on a wave to the same point on the next wave
What is frequency?
The no. of waves passing a point per second (hertz)
What is a time period?
Time taken for a single wave to pass a point
What is wavespeed?
The distance travelled by a wave each second
What is the formula for wavespeed?
Wavespeed= Frequency x wavelength
How do we find the speed of sound using two wooden blocks?
Person 1 stands (holding wooden blocks) 100m away from Person 2. Person 2 starts a stopwatch when they see P1 about to hit the blocks-when P2 hears the noise they stop the stopwatch. Repeat this in time with the waves. Calc mean time.
S= D/t
How do we find the wave speed using two wooden blocks and a wall?
P1 stands 50m away from a wall next to P2 (holding a stopwatch). P1 claps the blocks and continues to clap in rhythm with the echoes. P2 times between claps- repeat+ find avg. S= (distance to wall)x2 / avg time between claps
How do we find wave speed using an oscilloscope?
Two microphones are 5 metres apart and attached to an oscilloscope (shows time taken). A sound is made and the oscilloscope shows the time taken for sound waves to reach microphones.
What does an oscilloscope show?
Shows waves on a screen and can tell us time taken for a wave to reach microphones.
How do we find wave speed in water?
Apparatus: Ripple tank with paper underneath + light shining on top. To find wavelength, take pic+ place ruler to measure. To find freq, record and count how may wave pass in 10 secs then divide by 10. Speed= wavelength x freq. Or select wave and record to see how long it takes to cover distance of ripple tank.
How do we measure wave speed in solids?
Set up apparatus, adjust the frequency of the signal generator until a “solid” wave is produced, once the “solid” wave is produced, record the frequency shown on the signal generator, use a ruler to measure wavelength, the length to measure will depend on the number of “solid” waves produced. Or measure the length of multiple wavelengths, and divide by the number of wavelengths seen, repeat+ adjust the frequency until another “solid” wave is produced
What is an electromagnetic wave?
Transverse waves that transfer energy from the source of waves to an absorber
What are the properties of EM waves?
Transverse, all travel at same speed in vacuums
What properties is the EM wave spectrum arranged in?
Wavelength (H-L)
Frequency (L-H)
What are the EM waves?
Radio, Micro, Infrared, Visible light, UV, X_rays, Gamma
What does a higher frequency mean in waves?
Higher energy, which means highly ionizing so harmful to cells, causing mutations/cancer.
What is visible light?
Range of waves visible to the human eye. Red (Lowest freq) , Orange, Yellow, Green, Blue, Indigo, Violet (Highest freq)
What is EM radiation?
An energy transfer pathway
What do shorter wavelengths mean?
Higher frequency= higher energy, more ionising and harmful. (UV, X-rays, Gamma)
Explain energy transfer by microwave ovens.
Water molecules can absorb some wavelengths of microwaves, so energy is transferred by radiation to the thermal energy of the food.
Explain energy transfer by infrared waves.
All hot objects emit infrared radiation, these waves can be absorbed by other objects (heating them)
Explain energy transfers from the sun.
The sun emits: UV (burns/tans), Infrared (heats), and visible light (allows us to see). All transferred by radiations.
What can happen when EM waves move from one medium to another?
They may be: Transmitted, Absorbed, Reflected or refracted.
Why do different materials react differently with different EM waves?
The different wavelengths and densities of the materials.
Define refraction.
The bending of waves due to switching mediums, so the wave travels at a different speed.
What causes refraction?
When a wave enters a different medium, the different parts of the wave enter at different times, leading to a change in speed- causes wave to bend.
When a wave moves from a more dense to a less dense, does it move closer or away from the normal?
Away from the normal- speeds up.
When a wave moves from a less dense to a more dense, does it move closer or away from the normal?
Towards the normal- slows down.
RP10: How do we investigate the amount of infrared radiation absorbed by different coloured surfaces?
Method: Set up identical flasks (diff colors: matt black, shiny black, grey, silver) fill them with hot water and measure start temp. Then start stopwatch +measure temps at regular intervals. Greatest heat loss= best emitter. Or use Leslie’s cube + infrared detector.
What happens when an atom absorbs EM waves?
The electrons gain energy and move to a higher energy level (outer shell)
What happens when an atom emits an EM wave?
The electrons have lost energy and move to a lower energy level (inner shell)
How can higher energies (gamma rays) be achieved by an atom?
When an EM wave interacts with the nucleus.
How are radio waves produced?
By connecting an antenna to a high frequency ac current power source.
What happens in the transmitting antenna and receiving antenna when producing radio waves?
Transmitting: The charge from the ac oscillates up and down the antenna, this produces radio waves.
Receiving: Metal aerial absorbs these radio waves, creating an ac with the same frequency as transmitted waves.
What are the dangers of high energy EM waves?
Frequency is high, so energy is high. This makes them ionising which damages cells, causing mutations and caner.
Define radiation dose.
A measure of the risk of harm resulting from exposure of ionsing radiation. (Sieverts)
What are the dangers of radio waves?
No known danger.
What are the dangers of infrared waves?
Skin burns
What are the dangers of visible light?
bright lights causing eye damage
What are the dangers of microwaves?
certain frequencies can be absorbed by water molecules, human body contains lots of water so possible heat damage to internal organs.W
Why are microwave ovens considered to be safe?
Although they emit large amounts of microwaves, the glass door and metal walls prevent them from escaping.
What are the dangers of UV waves?
High energy= ionising so they can kill skin cells and cause premature aging- skin cancer.
Can cause severe eye damage.
What are the dangers of X-rays and gamma rays?
Most ionising and penetrate+ damage cells. Cause mutations and cancer.
Where are the uses radio waves?
Communication (radios/TV)
What are the uses of micrwaves?
Heat food, remotes, electric heaters and infrared cameras
What are the uses of visible light?
Taking photos/videos, fibre optic
What are the uses of UV waves?
Tans, security markings, fluorescent bulbs
What are the uses of X-rays?
X-ray images in medicine/security.
What are the uses of gamma rays?
Sterilize medical equipment + treats cancer.
Why are radio waves suitable for long range communication?
Can be reflected from the Earth’s atmosphere
Why are microwaves suitable for satellite communication?
Can penetrate the Earth’s atmosphere
Why are infrared waves suitable for fibre optic communication?
Can undergo total internal reflection
Why is visible light suitable for taking photos/videos?
Cameras are set up to detect visible light.
Why are UV rays suitable for detecting security ink?
Ink fluoresces with UV light.
Why are X-rays suitable for showing images of bones?
They can penetrate through soft tissues but not bones.
Why are gamma rays suitable for sterilising medical equipment?
They kill bacteria
