Section 3 - Waves Flashcards
What is wavelength(λ)?
The distance from one peak to the next
What is frequency(f)?
The number of complete waves per second
What is amplitude?
The height of the wave, from the rest(middle of graph) to the crest
What is the period(T)?
The time it takes for one complete wave to pass a point
What is the formula for frequency?
f = 1/T
What is the formula for the velocity of a wave?
v = f*λ
Ratio of kHz to Hz
1 : 1000
Ratio of MHz to Hz
1 : 1000000
Examples of transverse waves
Light, EM waves, ripples on water
Examples of longitudinal waves
Sound/ultrasound, shock waves
Definition of a transverse wave
The vibrations are at 90° to the direction energy is transferred by the wave
Definition of a longitudinal wave
The vibrations are along the same direction as the wave transfers energy
What do(and don’t) waves transfer?
Energy and information, but without transferring matter
How can the direction of travel of waves be changed?
Waves can be reflected, refracted and diffracted
What is reflection?
The wave rebounds off the object
What is refraction?
The wave goes through the object but changes direction
What is diffraction?
The wave spreads out when the pass through a gap or past the edge of an object
The 7 electromagnetic waves
- Radio waves
- Microwaves
- Infra-red
- Visible light
- Ultra-violet
- X-rays
- Gamma rays
Which wave has the highest frequency and lowest wavelength?
Gamma rays
Which wave has the lowest frequency and the highest wavelength?
Radio waves
Colours of visible light
Red, Orange, Yellow, Gave, Blue, Indigo, Violet
Richard Of York Gave Battle In Vain
Use of radio waves
Communication
Use of microwaves
Satellite communication(shorter wavelength can pass easily through the atmosphere)
Use of infrared radiation
Electrical radiators and night-vision equiptment
Use of visible light
Communication through optical fibres/photography
Use of ultraviolet
Fluorescent lamps
Use of X-rays
Viewing internal structures of objects and materials
Use of gamma rays
Sterilising medical equipment/food
Danger of microwaves
Internal heating of body tissues
Danger of infrared radiation
Skin burns
Danger of visible light
Eye damage
Danger of ultraviolet light
Damage of surface cells(cancer)
Skin burns
Blindness
Danger of X-rays
Cancer caused by long term exposure
Danger of gamma rays
Cell mutation/cancer
Law of reflection
Angle of incidence = Angle of reflection
Where are the angles of incidence and reflection defined?
Between the ray and the normal - NOT between the ray and the surface
Definition of the normal
An imaginary line at right angles to the surface(goes in both directions - both into the mirror and out of it)
Three points of a virtual image
- The image is the same size as the object
- The image is as far behind the mirror as the object is in front
- The image is formed from diverging rays
- Look at p 36 for how to answer the question
What happens if a wave hits a different medium face on?
The speed changes but the speed remains the same
What happens if a wave hits a different medium at an angle?
The speed changes and the wave is refracted
When light passes into a denser medium…
it bends towards the medium
When light passes a less dense medium…
it bends away from the medium
A wave bends towards the normal because…
it slows down
A wave bends away from the normal because…
it speeds up
A triangular prism disperses white light because…
it doesn’t have parallel boundaries
Formula for refractive index
n = c(speed of light in vacuum) / v(speed of light in material)
Speed of light in a vacuum
c = 3 * 10⁸ m/s
Snell’s law
When an incident ray passes into material:
n = Sin(i) / Sin(r)
How to find the refractive index of glass using a glass block
Page 38
Critical angle
When the angle of incidence results in r = 90°
Above the critical angle…
total internal reflection occurs - no light leaves the medium
How to investigate the critical angle
Page 39
Using Snell’s law to find critical angles
Sin(C) = 1 / n
Optical fibres
- Made of plastic or glass
- Consist of a central core surrounded by cladding that has a lower refractive index
- The core is so narrow that light passing through it hit the core-cladding boundary at angles higher than C
- Therefore the light is always totally internally reflected
Analogue signals
Can take any value within a certain rage
Digital signals
Can only take two values(on/off)
What happens to analogue and digital signals as they travel?
- They weaken, and therefore need to be amplified along their route
- They pick up interference/noise from electrical disturbances and other signals
Multiplexing
Transmitting multiple signals at the same time with just one cable/EM wave - easier with digital sounds
Quantisation
Rounding multiple values to a smaller set: more data is lost with an analogue signal than a digital signal
When sound waves enter a denser medium…
they speed up and refract
How to measure sound waves
Connect a sound wave receiver(such as a microphone) to an oscilloscope
Measuring the speed of sound using an oscilloscope
Page 42
