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
What happens when the wave is absorbed by the second material?
The wave is ABSORBED by the second material - the wave transfers energy to the material’s energy stores. Often, the energy is transferred to a thermal energy store, which leads to heating (this is how a microwave works, see page 223).
What happens when the wave is transmitted by the second material?
The wave is TRANSMITTED through the second material - the wave carries on travelling through the new material. This often leads to refraction (see p.221). This can be used in communications (p.222) as well as in the lenses of glasses and cameras. This is due to the fact that there is a difference in the velocity of the waves in different substances
What happens when the wave is reflected by the second material?
The wave is REFLECTED - this is where the incoming ray is neither absorbed or transmitted, but instead is ‘sent back’ away from the second material. This is how echoes are created.
Note:
AQA says that student should be able to construct ray diagrams to illustrate the refraction of a wave of a boundary between two different media, (check page 221)
Note:
AQA says that student should be able to use wave front front diagram to explain refraction in terms of the change of speed that happens when a wave travels from one medium to a different medium (check page 221)
Practical 21
AAAA
How can you produce radio waves?
You can produce radio waves using an alternating current in an electrical circuit. The object in which charges (electrons) oscillate to create the radio waves is called a transmitter.
When radio waves are absorbed what happens?
When radio waves are absorbed, they may create an alternating current of the same frequency is the radio wave itself, so radio waves kind of cells induce oscillations in an electrical circuit
What do changes in atoms and the nuclei of atoms result in for electromagnetic waves?
Changes in atoms, and the nuclei of atoms can result in electromagnetic waves being generated or absorbed over a white frequency range. Gamma rays originate from the changes in the nucleus of an atom
Why do ultra-violet waves, x-rays and gamma rays have a chance of having a hazardous effect on human body tissue?
The effects depend on the type of radiation and the size of the dose. Radiation dose (in sieverts) is a measure of the risk of harm resulting from an exposure of the body to the radiation.
What is 1000 millisieverts equal to?
1 Sievert
State the risks and consequences of exposure to radiation
Eyes - High doses can cause cataracts.
Thyroid - Radioactive iodine can build up and cause cancer, particularly during growth.
Lungs - Breathing in radioisotopes can damage. DNA.
Stomach - Radioactive isotopes can sit in the stomach and irradiate for a long time.
Reproductive organs - High doses can cause sterility or mutations.
Skin - Radiation can burn skin or cause cancer.
Bone marrow - Radiation can cause leukaemia and other diseases of the blood.
What can ultra-violet waves cause?
They 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 the mutation of jeans and cancer
Why each type of electromagnetic wave is suitable for the practical application
It is important that you are able to explain why each type of EM wave is suitable for the practical application. Since each part of the EM spectrum has different wavelengths, frequencies and energies it allows them to have different uses or functions. All of the uses or functions depend on the how well the receiving end can absorb, reflect, transmit or refract the wave. Cooking food is to do with absorption whereas fibre optic communications is reflection.
