Waves Flashcards
How do you measure the speed of sound in air? What is the accepted value?
- An observer with a stop watch stands 100m away from someone with a starting pistol.
- The observer records the time period between them seeing the person raise their hand as they fire the pistol and hearing the sound.
- Distance/time = speed, so 100/time=speed.
330m/s.
RP8: Measure frequency, wavelength and wave speed of waves on a water surface using a ripple tank.
- Set up a ripple tank (a transparent shallow tray of water with a light shining down through it onto a white card below in order to clearly see the motion of the ripples created on the water’s surface) with 5cm of water and a motor and wooden rod to create regular waves hovering just above the water.
- Switch on the lamp and motor, adjust until low frequency waves can be observed.
- Measure the length of a number of waves, then divide by the number of waves to calculate wavelength.
- Count the number of waves passing a point in 10 seconds then divide that by 10 to get frequency.
- Wave speed = frequency * wave length.
Systematic error:
Random error: incorrect measurement of wavelength, not 10 seconds.
Hazards: Electrical components near water.
Risks: Shocks and damage to components.
Precautions: Secure electrical components first and take care not to splash.
RP8: Measure frequency, wavelength and wave speed of waves in a solid.
- Attach a string or cord to a vibration generator and use a 200 gram (g) hanging mass and pulley to pull the string taut over the edge of the bench. Place a wooden bridge under the string near the pulley.
- Switch on the vibration generator and adjust the wooden bridge until stationary waves can be easily observed.
- Measure the length of as many half wavelengths (loops) as possible, divide by the number of half wavelengths (loops). This is half the wavelength, doubling this gives the wavelength.
- The frequency is the frequency of the power supply.
- Wave speed = frequency × wavelength.
Systematic error: incorrect frequency on power supply.
Random error: incorrect ruler readings.
Hazards: Cord.
Risks: Cord snapping and damaging eyes.
Precautions: Eye protection, screen.
What is the normal human hearing range and why is it restricted?
20 - 20,000 Hz.
What are the uses of ultrasound technology, why do they work, what is the frequency of ultrasound?
Medical: breaking kidney stones, imaging.
Industrial: images of defects inside parts.
They are partially reflected at boundaries, and the vibrations can shake and break objects.
20,000Hz/20kHz.
Compare p and s waves.
S waves are transverse, slower and can only travel through solids.
P waves are longitudinal, faster and can travel through solids and liquids.
S waves aren’t detected on the other side of the Earth from an earthquake, so therefore they must not be able to pass through the outer core so it must be liquid.
P waves are detected on the other side, but the size and position of two shadow zones suggest they are refracted within a solid inner core.
RP9: Investigate the reflection and refraction of light by different mediums.
- Trace around an acrylic polymer block, draw on a normal at 90 degrees to the block all on white paper.
- In a dark room, shine a ray of light from a ray box at the intersection of the block and normal. This is the incident ray.
- Mark on in pencil the centre of the reflected ray and the refracted ray where it leaves the block on the other side.
- Remove the block and join the marks to draw on the reflected ray and join up the normal to where the refracted ray leaves the block, and then beyond the block along the rest of the refracted ray.
- The angle between the normal and reflected ray is the angle of reflection and it should equal the angle of incidence. The angle between the normal and refracted ray through the block is the angle of refraction. Measure all angles.
- Repeat with a glass block.
Systematic errors: the light ray must stay at the same angle of incidence for both blocks.
Random errors: not measuring angles correctly with the protractor.
Hazards: Ray box gets hot, semi-dark environment.
Risks: Minor burns, trip hazard.
Precautions: Do not touch bulb and allow time to cool, ensure environment is clear of trip hazards before lowering lights.
How do radio waves link to electrical circuits?
Radio waves can be produced by oscillations in electrical circuits. When radio waves are absorbed they may create an alternating current with the same frequency as the radio wave itself, so radio waves can themselves induce oscillations in an electrical circuit. Information can be coded into them before transmission, then decoded later.
Which waves are hazardous and how?
UV, X-ray, Gamma.
Ultraviolet waves can cause skin to age prematurely and increase the risk of skin cancer. X-rays and gamma rays are ionising radiation that can cause the mutation of genes and cancer.
The effect depends on the type of radiation and size of dose.
What are the uses of the waves and how are they suitable?
Radio waves - tv and radio. They can be reflected, transmit through air and don’t harm the human body.
Microwaves - heating food, satellite communications. At high frequencies they are easily absorbed by food molecules whose internal energy increases and they pass easily through the atmosphere.
Infrared - electrical heaters, infrared cameras, cooking food. All objects emit infrared, some chemical bonds absorb infrared and their internal energy increases.
Visible light - fibre-optic communications, coded pulses of light travel from glass fibres from a source to a receiver.
Ultraviolet - tanning, lights. Fluorescent substances absorb ultraviolet light produced inside the lamp, and re-emit the energy as visible light.
X-rays and Gamma - medical imaging and treatments. Both transmit mostly through the body, x-rays are absorbed by dense structures like bones.
Can you draw convex and concave ray diagrams and label them?
Check it.
Can you draw and interpret diagrams depicting the affect of radiation Earth’s temperature?
Check it.
RP10: Investigate how the amount of infrared radiation absorbed or radiated by a surface depends on the nature of that surface.
- Place a Leslie cube on a heat-resistant mat. Fill it, almost to the top, with boiling water and replace the lid.
- Leave for one minute. This is to enable the surfaces to heat up to the temperature of the water.
- Use the infrared detector to measure the intensity of infrared radiation emitted from each surface, or the temperature of the surface. Make sure that the detector is the same distance from each surface for each reading.
- Plot a bar chart to show the results of each material. In order of best to worst emitter: matt black, shiny black, matt white, shiny silver.
Systematic error: zero error.
Random error: held at various distances, not leaving it for one minute so the results are not distinct.
Hazards: boiling water.
Risks: scalding, burns.
Precautions: pour water slowly, do not move Leslie cube until it has fully cooled.
