P6 Flashcards
(36 cards)
amplitude
Of a wave is the maximum displacement of a point on the wave from its undisturbed position.
wavelength
The distance between the same point on 2 adjacent waves.
frequency
The no. of complete waves passing a certain point per second.
Measured in hertz. 1Hz is 1 wave per second.
From frequency you can find period of a wave using amount of time it takes for a full cycle of the wave.
Transverse Waves
The oscillations (vibrations) are perpendicular (at 90 degrees) to the direction of energy transfer. eg: all electromagnetic waves, ripples and waves in water, a wave on a string.
Longitudinal Waves
The oscillations are parallel to the direction of energy transfer.
eg: sound waves in air.
wave speed
The speed at which energy is being transferred (or speed the wave is moving at). wave speed (m/s)= frequency (Hz) x wavelength (m)
Oscilloscope practical 1
- set up oscilloscope so detected waves at each mic are shown as separate waves.
- start with both mics next to speaker, then slowly move 1 away until the 2 waves are aligned on display, but have moved exactly 1 wavelength apart.
Oscilloscope practical 2
- measure distance between mics, find 1 wavelength.
- use formula to find speed of sound waves passing through air-frequency is what you set signal generator to.
- speed of sound in air= 330m/s, check results match.
Water waves practical 1
- using signal generator attached to dipper of a ripple tank, you create water waves at set frequency.
- dim lights in lab & turn on lamp. Should see wave crests as shadows on screen below tank.
Water waves practical 2
- distance between each line=1 wavelength. Measure distance between shadow lines that are 10 wavelengths apart, then divide this distance by 10 to find average wavelength.
- use method to calculate wave speed of the waves.
- this set up is good as it allows you to measure wavelength without disturbing waves.
Waves on string practical 1
- set up equipment. Turn on signal generator and vibration transducer. String will start to vibrate.
- adjust frequency of signal generator until there’s a clear wave on string. Frequency you need will depend on length of string between pulley & transducer, and masses you’ve used.
Waves on string practical 2
- measure wavelength of these waves. To do this accurately: measure lengths of 4or5 half wavelengths in one go, then divide to get mean half wavelength. Then double mean to get full wavelength.
- frequency of wave=what signal the generator is set to.
- find speed using formula.
Wave meeting a boundary (3 options)
ABSORBED by the 2nd material. Wave transfers energy to material’s energy stores. Often energy goes to thermal energy store, leads to heating.
TRANSMITTED through. Wave carries on travelling through material. Often leads to refraction.
REFLECTED. Incoming ray is sent back from second material. How echoes are created.
Electromagnetic Waves
All travel at same speed through air or a vacuum.
Vibrations of electric + magnetic fields.
Travel at different speeds in different materials.
Vary in wave length (10 to the -15 to more than the 4.
Generated by a variety of changes in atoms+nuclei.
EM wave examples
Camp fire transfers energy to surroundings by emitting infrared radiation. These waves are absorbed by objects + transfer energy to objects thermal store, so object warms up.
Radio waves transfer energy to KE stores of electrons in radio receivers, generates electric current.
Refraction
When wave crosses boundary between 2 materials it changes speed. If wave hits boundary at an angle it changes direction - its refracted.
Wave bends towards normal if slows down, bends away from normal if speeds up.
How much something is refracted
Depends on how much wave speeds up/slows down, which depends on density of the 2 materials (higher density, slower a wave travel through).
Wavelength changes when refraction happens.
Optical density
Measures how quickly light travels through it - higher optical density, slower light waves travel through it.
Ray diagrams
- Draw boundary between 2 materials + the normal (the imaginary line perpendicular to where incoming wave hits boundary)
- Draw incident ray that meets normal at boundary.
- Angle between ray + normal is angle of incidence. Draw with protractor if given an angle.
- Draw refracted ray on other side of boundary.
- Angle of refraction is angle between refracted ray and the normal.
Wave front
A line showing all the points on a wave that are in the same position as each other after a given no. of wavelengths. Wave crosses boundary at angle, only part of wave front crosses boundary at first.
Denser material=slower travel.
By the time whole wave front crosses boundary, faster part of it will have traveled further than slower part. Difference in distance traveled causes wave to refract.
Uses of EM waves
Radio waves: bluetooth, TV and FM radio.
Microwaves: satellites (satellite TV).
Infrared: infrared cameras electric heaters.
Visible light: optical fibres.
Ultra violet: fluorescent lights, security pens.
X-rays + gamma rays: radiographers in hospitals.
Leslie Cube practical
Place empty leslie cube on heat proof mat.
Boil water, fill leslie cube with it.
Cube warms up, all 4 faces should have same temp.
Hold infrared detector a set distance from 1 of vertical faces. Record amount of IR radiation it detects.
Repeat measurement for each face.
More IR radiation will be detected from black rather than white or matte surfaces rather than shiny.
Melting wax practical
- Set up equipment. 2 ball bearings stuck to one side of metal plate with solid bits of candle wax. Other side of plates face towards flame.
- Sides of plates facing towards flame each have a different surface colour.
- Ball bearing on black plate will fall first as surface absorbed more IR radiation - transferring more to TE store of wax. Wax on black plate melts before wax on silver plate.
Risk of EM waves
Low frequency waves pass through soft tissue without being absorbed.
High frequency waves all transfer lots of energy so cause lots of damage.
UV radiation damages surface cells, lead to sunburn and skin cancer.
X-rays and gamma rays are ionising, cause gene mutation or cell destruction, even cancer.