Topic 3 - Waves Flashcards
What is the difference between longitudinal and transverse waves?
Longitudinal waves vibrate parallel to the direction of travel
Transverse waves vibrate at a right angle to the direction of wave travel
What is amplitude?
The distance from the centre line to the top of a crest.
What is wavefront?
A line showing points that are in the same phase of a wave (e.g peak or trough)
What is frequency?
The number of waves that pass a point each second
What is wavelength?
The distance between a point on one wave and the same point on the next wave.
What is the period of a wave?
The time it takes for one complete wave to occur / the time it takes for one wave period to occur
The equation is wave speed = frequency x wavelength (v = f x λ), but what are the units and rearrangements?
v = f x λ
f = v / λ
λ = f / v
v = wave speed (m/s)
f = frequency (hertz, Hz)
λ = wavelength (metres, m)
The equation is frequency = 1 / time period (f = 1 / t), but what are the units and rearrangements?
f = 1 / t
t = 1 / f
1 = f x t
f = frequency (Hertz, Hz)
t = time period (seconds, s)
What is the Doppler effect?
If an object is moving, waves in front of it are compressed, creating a shorter wavelength and higher frequency.
Waves behind it are spread out as it is moving away from previous wavefronts, this creates a longer wavelength and lower frequency.
What can all waves be?
Reflected and refracted.
What are 2 similarities among all electromagnetic waves
They all travel at the same speed, the speed of light (3x10⁸)
They are all transverse (vibrate perpendicular to direction of wave travel)
What is the order of the electromagnetic spectrum in order of decreasing wavelength and increasing frequency?
Radio Waves –> Microwaves –> Infrared –> Visible light –> UV –> X-rays –> Gamma rays
What is the order of visible light in terms of decreasing wavelength?
Red
Orange
Yellow
Green
Blue
Indigo
Violet
What are two uses of each of the electromagnetic waves?
Radio waves - broadcasting and communications
Microwave - Cooking and satellite transmissions
Infrared - Heaters and night vision equipment
Visible light - Seeing and photography
UV - Fluorescent lamps and disinfection
X-rays - Checking for breaks/fractures, scanning luggage
Gamma rays - Sterilising food and cancer treatment (Radiotherapy)
What are the effects of excessive exposure to:
Microwaves
Infrared
UV
Gamma Rays
Microwaves - Internal heating of body tissue
Infrared - Skin burns
UV - Damage to surface cells and blindness
Gamma rays - Cancer, mutation
What is the problem with UV, X-rays and gamma rays?
They are ionising, and too much exposure to them can cause your cells to mutate, and you can develop cancer.
What type of wave is light?
Light is a transverse wave, and can be reflected and refracted.
What is the law of reflection?
Angle of incidence = Angle of reflection
i = r
What is a ray diagram?
A diagram that shows the path of a light ray through reflection or refraction.
What is refractive index?
A measure of how much an object bends/slows light when it enters the object from air.
The equation for refractive index is n = sin(I) / sin(r), but what are the units and rearrangements?
n = sin(i) / sin(r)
i = sin⁻¹(n x sin(r))
r = sin⁻¹(sin(i) / n)
n = refractive index (no units)
sin(i) = sin(angle of incidence) (°)
sin(r) = sin(angle of reflection) (°)
What is the critical angle?
The angle of incidence which creates an angle of refraction of 90°
What is total internal reflection? When can it occur?
Where the angle of incidence is greater than the critical angle, meaning the light will bounce back instead of refracting out.
This can only occur when going from a higher refractive index (denser object) to a lower one (less dense object), e.g. water to air.
How does total internal reflection occur in optical fibres?
Light is sent along the fibre core, which is a thin glass or plastic strand.
The core has a higher refractive index than the outer cladding.
This means that when going around a curve, the light hits the wall of the core at a higher angle than the critical angle.
Total internal reflection will occur, so the light bounces down the fibre, staying trapped inside.
This lets the signal move through curves and long distances with little energy loss.
