P6 Flashcards
What are all waves?
They are either transverse or longitudinal
What is a transverse wave?
In transverse waves, the oscillations (vibrations) are perpendicular (at 90° to the direction of energy transfer. In simple terms, they have sideways vibrations
What is a longitudinal wave?
In longitudinal waves, the oscillations are parallel to the direction of energy transfer. In simple terms, they have parallel vibrations
What are examples of a transverse wave?
1) All electromagnetic waves, e.g. light
2) Ripples and waves in water
3) A wave on a string
What are examples of a longitudinal wave?
An example is sound waves in air
Explain what happens when waves travel through a medium
When waves travel through a medium, the particles of the medium oscillate and transfer energy between each other (see p.167). BUT overall, the particles stay in the same place - only energy is transferred.
For example, if you drop a twig into a calm pool of water, ripples form on the water’s surface. The ripples don’t carry the water (or the twig) away with them though.
What is the amplitude of a wave?
The amplitude of a wave is the maximum displacement of a point on the wave from its undisturbed position
What is the wavelength of a wave?
The wavelength is the distance between the same point on two adjacent waves (e.g. between the through of one wave and the through of the wave next to it)
What is the frequency of a wave?
Frequency is the number of complete waves passing a certain point per second. Frequency is measured in hertz (Hz). 1 Hz is I wave per second.
What is the period of a wave?
The ‘period’ of a wave is more commonly known as the ‘time period’. This is the amount of time it takes for a complete wave to occur. We know that frequency is the number of waves passing a point in one second.
Note:
A QA says that student should be able to describe wave motion in terms of the amplitude, wavelength, frequency, and period
How do you find the period of a wave?
Period(s) = 1/Frequency (Hz)
T = 1/f
(On physics equation sheet)
What is the wave speed?
The wave speed is the speed at which the energy is transferred (or the wave moves) through the medium.
How do you find wave speed?
Wave speed(m/s) = Frequency(Hz) x Wavelength(m)
v = fλ
Note:
AQA says that students must identify amplitude and wavelength from given diagrams (check page 218 for this)
State the method to find the speed of sound waves in the air
By attaching a signal generator to a speaker you can generate sounds with a specific frequency.
You can use two microphones and an oscilloscope to find the wavelength of the sound waves generated.
1) Set up the oscilloscope so the detected waves at each microphone are shown as separate waves.
2) Start with both microphones next to the speaker, then slowly move one away until the two waves are aligned on the display, but have moved exactly one wavelength apart.
3) Measure the distance between the microphones to find one wavelength (2)
4) You can then use the formula v = f2 (p.218) to find the speed (v) of the sound waves passing through the air - the frequency (f) is whatever you set the signal generator to (around 1 kHz is sensible).
5) The speed of sound in air is around 330 ms, so check your results roughly agree with this.
State a method to measure the speed of ripples on a water surface
1) Using a signal generator attached to the dipper of a ripple tank you can create water waves at a set frequency (f).
2) Dim the lights in the lab and turn on the lamp. You should see the wave crests as shadows on the screen below the tank.
3) The distance between each shadow line is equal to one waveleneth.
Measure the distance between shadow lines that are 10 wavelengths apart, then divide this distance by 10 to find the average wavelength.
4) This is a good method for measuring the wavelength of moving waves (p.233) or small wavelengths.
5) Use v = f7 to calculate the wave speed of the waves.
6) This set-up is suitable for investigating waves, because it allows you to measure the wavelength without disturbing the waves.
Practical 20:
AAAA
What are electromagnetic waves?
Electromagnetic waves are transverse waves that transfer energy from the source of the waves to absorber
Electromagnetic waves form a continuous spectrum and all types of electromagnetic waves travel at the same velocity for a vacuum(space) or air
For waves that form the electromagnetic spectrum, how are they grouped?
The waves that form the electromagnetic spectrum are grouped in terms of the wavelength and frequency.Going from long to short wavelength (or from low to high frequency). The groups are radio microwaves infrared infrared visible light (red to Violet), ultraviolet, x-rays and gamma rays.
What if the EM wave is not in the groups?
We put them into different groups forming, a continuous spectrum
Why do our eyes only detect a limited range of electromagnetic waves?
As our eyes only detect, visible light and so detect a limited range of electromagnetic waves
Examples that illustrate the transfer of energy by electromagnetic waves
radio waves – television and radio (including Bluetooth)
microwaves – satellite communications, cooking food.
infrared – electrical heaters, cooking food, infrared cameras.
visible light – fibre optic communications.
ultraviolet – energy efficient lamps, sun tanning.
X-rays – medical imaging and treatments.
When a wave meets a boundary between two materials, what three things can happen?
The wave is either absorbed,transmitted or reflected