P6 - Waves Flashcards
What can waves be?
Transverse or longitudinal
Example of a transverse wave
The ripples on a water surface - it is the wave that travels and not the water
What do longitudinal waves show
Compression and rarefaction
Examples of a longitudinal wave
Sound waves travelling through air - it is the wave that travels and not the air itself
What is the difference between transverse and longitudinal waves (3)
- In transverse waves the oscillations (vibrations) are perpendicular (at 90°) to the direction of energy
- Where as in longitudinal waves, the oscillations are parallel to the direction of energy transfer
What is the amplitude of a wave
Is the maximum displacement of a point on a wave away from its undisturbed position
What is the wavelength of a wave
Is the distance from a point on one wave to the equivalent point on the adjacent wave
What is the frequency of a wave
Is the number of waves passing a point each second
Equation for period
Period(s) = 1/frequency (Hz)
Equation for frequency
Frequency = 1/period (s)
What is wave speed
Is the speed at which the energy is transferred (or the wave moves) through the medium
The wave equation that all waves obey
Wave speed (m/s) = frequency (Hz) x wavelength (m)
Wave diagram
Check photos
Describe a method to measure the speed of sound waves (3)
- set up an oscilloscope so the detected waves at each microphone are shown as separate waves
- start with both mics next to the speaker, then slowly move away until the two waves are aligned on the display, but have moved exactly one wavelength apart
- Measure wavelength - then use the wave speed formula
Measure the frequency, wavelength and speed of waves in a ripple tank - required practical (apparatus) (5)
- Lamp
- Dipper
- Water
- Signal generator
- Metre ruler
Measure the frequency, wavelength and speed of waves in a ripple tank - required practical (method) (4)
- Using a signal generator attached to the dipper of a ripple tank you an create water waves at a set frequency
- Dim the lights and turn on lamp - should see wave crests as shadows on the screen below
- The distance between each line is the wavelength - find the average wavelength after 10 lines
- Use the equation wave speed = wavelength x frequency
Measure the frequency, wavelength and speed of waves in a solid - required practical (apparatus) (6)
- Vibration transducer
- String
- Pulley
- Signal generator
- Bench
- Masses
Measure the frequency, wavelength and speed of waves in a solid - required practical (method) (4)
- Adjust the frequency of the signal generator until there’s a clear wave on the string - frequency will depend on the length of string between the pulley and the transducer, and the masses you’ve used
- the best way to measure the wavelength is to measure lengths of 4 or 5 half wavelengths in one go then get an average then double to get a full wavelength
- The frequency is whatever the signal generator is set to
- You can find the speed using the wave speed = wavelength x frequency equation
Electromagnetic waves (3)
- Are transverse waves that transfer energy from the source of the waves to an absorber
- Form a continuous spectrum
- All types of electromagnetic wave travel at the same velocity through a vacuum or air
How are the waves that form the electromagnetic spectrum grouped
In terms of their wavelength and their frequency - going from long to short wavelength or from low to high frequency
Groups in the electromagnetic spectrum (7)
Radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays
What do our eyes only detect
Visible light - so detect a limited range of electromagnetic waves
Example of transfer of energy by electromagnetic waves (camp fire)
- A camp fire transfers energy to its surroundings by emitting infrared radiation
- These infrared waves are absorbed by objects and transfer energy to the object’s thermal energy store, causing the object to warm up
Example of transfer of energy by electromagnetic waves (radio waves)
Radio waves transfer energy to the kinetic energy store of electrons in radio receivers, which generates
What may different substances do with electromagnetic waves (2)
- Different substances may absorb, transmit, refract or reflect electromagnetic waves in ways that vary with wavelength
- Some effects e.g refraction are due to the difference in velocity of the waves in different substances
Explain refraction using wave front diagrams (2)
- When a wave crosses a boundary at an angle, only part of a wave front crosses the boundary at first - if it’s travelling into a denser material, that part travels slower than the rest of the wave front
- So by the time the whole wave front crosses the boundary, the faster part of the wave front will have travelled further than the slower part of the wave front
- This difference in distance travelled (caused by difference in speed) by the wave front causes the wave to bend (refract)
Ray diagrams
Check photos
Investigating infrared radiation - required practical (apparatus) (4)
- Leslie cube
- Heat proof mat
- Boiled water
- Infrared detector
Investigating infrared radiation - required practical (method) (5)
- Place an empty Leslie cube onto a heat proof mat
- Fill Leslie cube with boiled water
- Wait for cube to warm up - hold thermometer against each side (should all be the same temp)
- Hold an infrared detector at a set distance (e.g 10cm) from one of the sides - then record the amount of IR radiation
- Repeat for each side
Investigating infrared radiation - required practical (results) (2)
- you should find that you detect more infrared radiation from the black surface than the white and more from the matt surface than the shiny ones
- Make sure results are repeatable
Investigating infrared radiation - required practical (safety) (2)
- Don’t try to move the cube when its full of boiling water as you might burn your hands
- Be careful when carrying a full kettle of boiling water
Radio waves (2)
- Can be produced by oscillations in electrical circuits
- When they 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
What can changes in atoms and nuclei of atoms result in
Can result in electromagnetic waves being generated or absorbed over a wide frequency range - gamma rays originate from changes in the nucleus
Effects of ultraviolet waves, X-rays and gamma rays
Hazardous effects human tissue - the effects depend on the type of radiation and size of the dose
Radiation dose (in sieverts) (2)
- Is a measure of the risk of harm resulting from an exposure of the body to the radiation
- 1000 millisieverts (mSv) = 1 sievert (Sv)
What can ultraviolet waves cause
Can cause skin to age prematurely and increase the risk of skin cancer
What can X-rays and gamma rays cause
They are ionising radiation that can cause mutation of genes and cancer
Use of radio waves
Television and radio - long wave radio can be transmitted from London and received halfway around the world also short wave radio signals can be received at long distances from the ionosphere
Use of microwaves
satellite communications and cooking food - travels a long distance and microwaves penetrate up to a few centimetres into the food before being absorbed and transferring energy
Use of Infrared
Electrical heaters, cooking food and infrared cameras - is given out by all objects and the hotter the object the more radiation it gives out
Use of visible light
Fibre optic communications - it is easy to refract light enough so that it remains a narrow fibre
Use of ultraviolet
Energy efficient lamps and sun tanning - UV radiation is absorbed then visible light is emitted
Use of X-rays and gamma rays
Medical imaging and treatments - pass through flesh easyily
