Chapter 13~waves 🌊 Flashcards
Definitions, key ideas 💡 and formulae
What are waves?
Waves are a means of transferring energy ⛮ or “information” from one point to another caused by vibrations. Also referred to as a periodic disturbance travelling through space, characterised by a vibrating medium.
Definition of progressive waves
A wave that carries energy ⛮ from one place/posifion to another through a material or vacuum.
Definition of a mechanical wave : and an example
°it is a wave that requires a material medium to move through, for example sound 🔊.
Definition of displacement :
The distance of a point on the wave 🌊 from its underdisturbed position or equilibrium position
Definition of amplitude, A:
The maximum displacement of any point on the wave from its underdisturbed position / equilibrium
A greater amplitude result in what for sound waves?
A louder sound 🔊
Definition of wavelength :
The distance from any point on a wave to the next exactly similar point, measured in metres. (e.g. From crest to crest)
Definition of period, T:
The time take for one complete oscillation of a point in a wave, measured in seconds.
The time taken for one wave /oscillation to pass a point.
The time taken for a particle to complete a full oscillation.
Definition of frequency, f :
The number of oscillation per unit time of a point in a wave, measured in hertz (Hz).
The number of waves/oscillations that pass a point per second.
A higher pitch is a result of..
A higher frequency
Definition of a longitudinal wave : and an example
Waves in which the particles of the medium vibrate parallel to the direction of the wave propagation (motion) or the wave velocity.
Example: sound 🔊
Definition of transverse waves :
Plus an example
Waves in which the particles of the medium vibrate at right angles or perpendicular to the wave motion /propagation /velocity.
Example : light wave
Frequency is the reciprocal of?
The period (T)
F= 1/T
Definition of compressions 🗜 :
A region in a longitudinal wave where the particles are closest together and where the air pressure is greater than its mean value.
Definition of rarefaction :
A region in a longitudinal wave where the particles are furthest apart and the air pressure is less than its mean value.
Definition of phase difference:
°the difference in the phases of 2 oscillating particles, experienced in degrees or radians. It also refers to the amount by which one wave leads or lags another wave.
How many degrees is equivalent 1 radian?
180°
Intensity of a wave 🌊 :
The rate of energy ⛮ transmitted per unit area at right angles to the wave velocity.
What are the units for intensity?
Watts per square metre, Wm-2
Formula for intensity
Intensity = power /cross-sectional area
The intensity of a wave generally decreases as it travels along for 2 reasons :
- The wave may ‘spread out’
2. The wave may be absorbed or scattered
Intensity is proportional to..
The square of the amplitude.
What is the wave equation and how is it derived in two steps?
v = f × ♈
v-velocity
F-frequency
♈-wavelength
Derived from :
Step 1 :
speed =distance / time
v= ♈÷ 1/T
Step 2 : rewrite this
v = ♈ x f
Bec 1/T =f
What is the Doppler effect?
The change in frequency or wavelength of a wave 🌊 observed when the source of the wave is moving towards or away from the observer (or the observer is moving relative to the source
Short meaning of the Doppler effect
It is the change in frequency due to the relative motion between the observer and source.
Formula for observed frequency =
f(o) =[f(s) v] /[v +/- v(s)]
When do you use a plus ➕ in the observed frequency formula?
This is used when either the observer / source is moving AWAY from the other
When do you use a minus ➖ in the observed frequency formula?
When there is movement towards of either the observer or source
What two things are unaffected by the movement of the source?
- The frequency f(s) of the source, it still emits f(s) waves per second
- The speed v of the waves
Definition of electromagnetic spectrum :
The family of transverse 🚦 waves 🌊 that travel through a vacuum at a speed of 3.00 × 10^8.
They are a group of waves with common properties
The five properties of electromagnetic waves 🌊 :
- All travel at the speed 🚤 of light 🚦
c= 3 × 10^8
Therefore (c =f ♈)
- All can be polarised
- All can be reflected, refracted, diffracted and absorbed
- All travel through a vacuum
- All can undergo interference
What are the seven electromagnetic waves? 🌊
In order of decreasing wavelength
- Radio waves
- Microwaves
- Infared
- visible
- Ultra-violet
- X-rays
- Gamma rays (y-rays)
What is the wavelength range in metres of radio 📻 waves?
> 10^6 to 10^-1
What is the wavelength range in metres of microwaves?
10^-1 to 10^-3
What is the wavelength range in metres of infared?♥
10^-3 to 7×10^-7
What is the wavelength range in metres of visible waves?
7×10 ^-7(red) to 4× 10^-7 (violet)
What is the wavelength range in metres of ultraviolet waves?
4 × 10^-7 to 10^-8
What is the wavelength range in metres of x-rays? ☠️💀
10^-8 to 10^-13
What is the wavelength range in metres of x-rays? ☠️💀
10^-8 to 10^-13
What is the wavelength range in metres of Y-rays ( gamma rays)?
10^-10 to 10^-16
State all 7 ranges of wavelengths from decreasing wavelengths :
R : >10^6 to 10^-1
M: 10^-1 to 10 ^-3
I: 10^-3 to 7 × 10^-7
V: 7 × 10^-7 (red) to 4 ×10 ^-7 (violet)
U: 4× 10 ^-7 to 10 ^-8
X : 10 ^-8 to 10^-13
Y: 10^-10 to 10 ^-16
Definition of an electromagnetic wave :
A disturbance in the electric and magnetic fields in space
What is polarisation?
It is the process in which transverse waves are restricted to vibrate in one plane (only)
