Waves Flashcards
What is Wavelength?
Distance from one peak to the next
What is Frequency?
- How many complete waves there are per second passing a certain point
- Measured in hertz
What is Amplitude?
Height of the wave from rest to crest
What is the Speed?
How fast the wave goes
What is the Period?
The time (s) it takes for 1 complete wave to pass a point
Wave speed =
Frequency x Wavelength
What are Examples of Transverse Waves?
- Light & EM waves
- Waves on strings
- Ripples on water
- Slinky spring going up & down
What are Examples of Longitudinal Waves?
- Sound & ultrasound
- Shock waves
- Slinky spring when push the end
Where are the Vibrations in Transverse Waves?
At 90 degrees to direction energy is transferred by wave
Where are the Vibrations in Longitudinal Waves?
Along same direction as wave transfers energy
What can Sound Waves make things do and give an example?
- Make things vibrate & move
* E.g. loud bangs can start avalanches
What can Waves be used as Signals to do and give an example?
- Used as signals to transfer info from one place to another
- E.g. light in optic fibres, radio waves travelling through air
What can All Waves do?
- Carry & transfer energy in direction they’re travelling
- Microwaves in oven make things hot, their energy transferred to the food your cooking
What are Wavefronts?
Imaginary planes cut across all waves, connecting points on adjacent waves that are vibrating together
What is the Doppler Effect?
- Makes waves appear longer or shorter
- Frequency of source moving towards you seem higher, wavelength seem shorter
- Frequency of source moving away from you seem lower, wavelength seem longer
What are the Electromagnetic Waves in order of increasing frequency and decreasing wavelength?
- Radio waves
- Microwaves
- Infrared
- Visible light
- Ultraviolet
- X-rays
- Gamma rays
What are all types of Electromagnetic waves and what do they all do?
- Transverse waves
* Travel at same speed through free space
What are Radio Waves used for and what is the Process?
- Tv and FM radio broadcasting
* Must be in direct sight of transmitter to get reception
What are Microwaves used for and what is the Process?
- Satellite communication
- Mobile phone calls from phone to nearest transmitter
- Cooking, microwaves absorbed by water molecules in food, penetrate few cm into food then absorbed, energy conducted to other part of food
What are Infrared Radiation used for?
- Electrical heaters
* Grills to cook food
What is Visible Light used for and what is the Process?
- Communication using optical fibres, carrying data over long distances as pulses of light - phones
- Photography, by varying aperture & shutter speed can capture as much light as you want
How do Optical Fibres work in Visible Light?
- Bounce waves off sides of narrow core
* Light enters fibre at one end, reflected until emerges at other end
What is Ultraviolet used for?
Fluorescent lights use UV to emit visible light
What are X-Rays used for and what is the Process?
- View internal structure of objects, materials, bodies
* X-ray directed through object/body onto detector plate
What are Gamma Rays used for and what is the Process?
- Sterilise medical instruments by killing all microbes
* Sterilise food by killing microbes so fresher for longer
How are X-Rays harmful?
Exposure to X-rays can cause mutations leading to cancer
What Electromagnetic radiation are usually more Dangerous?
Higher frequency - more energy so generally more harmful
How are Microwaves harmful and how can you Prevent this harm?
- Internal heating - heat human body tissue
* Prevent - microwave ovens need shielding
How are Infrared harmful and how can you Prevent this harm?
- Skin burns
* Prevent - Use insulating materials
How are Ultraviolet harmful and how can you Prevent this harm?
- Damage surface cells -blindness , cell mutation/destruction, cancer
- Prevent - wear sun cream, stay out of strong sunlight
How are Gamma harmful and how can you Prevent this harm?
- Ionising, a lot of energy
- Penetrate further into body
- Cell mutation/destruction - tissue damage, cancer
- Prevent - exposure time short, kept in lead lines boxes when not using
Angle of Incidence =
Angle of reflection
What is Diffuse Reflection?
Light reflects from uneven surface, light reflects of at all different angles = diffuse reflection
What is Clear Reflection?
Light reflects from even surface, all reflected at same angle = clear reflection
What is the Normal line?
Imaginary line that’s perpendicular to the surface at point of incidence
What is the Angle of Incidence?
Angle between the incoming wave and normal
What is the Angle of Reflection?
Angle between reflected wave and normal
How are Virtual Images Formed?
Light rays bouncing off object onto mirror are diverging, light from object appears to be coming from different place
How can Waves be Refracted?
- Wave hits boundary face on - slows down, carries on in same direction
- Wave meet at different medium at angle, hits denser later first then slows down, carries on at first - faster speed, wave changes direction = refracted
Why do Waves travel at different Speeds?
- Have different densities
- EM waves = slowly in denser media
- Sound waves = faster in denser substances
How do you draw a Ray Diagram for a Refracted Wave?
- Draw boundary (line) between 2 materials & normal
- Draw incident ray - meets normal at boundary
- Between Ray & normal = angle of incidence
- Refracted Ray on other side of boundary - denser = bends towards normal
- Between refracted Ray & normal = angle of refraction (smaller)
Explain how Rays passing through a glass box are Refracted Twice?
- Light ray at angle into block, light is reflected, most light goes through glass & refracted
- Trace incident & emergent rays onto paper
- Light passes from air to block(denser), bends towards normal(because slows down)
- Light to boundary on other side, speeds up because less dense, bends away from normal
- Light ray travel in same direction it was to begin with - refracted to normal & back again by same amount
What happens if you shine White Light into a Triangular Prism?
- Different wavelengths of light refract by different amounts
- White light goes into different colours as into prism - rainbow effect
Refractive Index (n) =
Speed of light in vacuum (c) / speed of light in that material (v)
n =
Sin i / Sin r
What does it mean if the angle of incidence is Less than Critical Angle?
Most light passes out but a little bit is internally reflected
What does it mean if the angle of incidence is Equal to Critical Angle?
Emerging Ray comes out along surface - a lot of internal reflection
What does it mean if the angle of incidence is Greater than Critical Angle?
No light comes out - all internally reflected - total internal reflection
Sin C =
1 / n
How do Optical Fibres use Total Internal Reflection?
- Have central core w/ lower refractive index
- Core of fibre narrow so light hit core-cladding boundary at angles above C
- Light always totally internally reflected
How do Prisms use Total Internal Reflection?
- Light onto prism, totally internally reflected at 90 degree
- Go to another prism lower down & totally internally reflected
- Ray travelling parallel to initial path
What are Sound Waves, how do they Act and what are they Caused by?
- Longitudinal waves
- Caused by vibrating objects
- Vibrations through surrounding medium as compressions
- Denser medium = faster sound
- Reflected by hard flat surfaces
- Refract as enter different media
How can you Display Sound Waves and what does it tell you?
- Oscilloscope- displays microphone signal as trace on a screen
- Tells you If loud/quiet, high/low pitched, compare frequency of waves
- High frequency = high pitched
What does it mean if the Sound wave has a Greater Amplitude?
- Carries more energy
* It will be louder
What does the horizontal axis on oscilloscope tell you?
Time
If 1 cycle crosses 20 division, what is the Period, if time division is set to 0.00001s?
20 x 0.00001s = 0.0002s
How do you use an Oscilloscope to Measure the Speed of Sound?
- Attach single generator to speaker - generate sound with specific frequency
- 2 microphones & oscilloscope
- Move microphones one wavelength apart
- Wavelength of sound waves generated = measure distance between microphones
- Use wave speed = freq x wavelength
