Section 3: Waves and EM spectrum Flashcards
What is frequency?
Number of complete waves passing a certain point per second.
Measured in Hertz (Hz)
1 Hz is one wave per second or
frequency = 1/time period
What is the period of a wave? (time period)
The time it takes for one complete wave to pass a point
What is amplitude?
The displacement of the wave from rest to crest
top/bottom from line
What is wavelength?
Distance from 2 exact points
e.g from crest to crest
What is diffraction?
The spreading out of a wave
- All waves spread out when they pass through a gap or an object
- Amount of diffraction depends on size of gap relative to wavelength of the wave.
- Narrower the gap/longer wavelength, more diffraction
- A narrow gap is about the same as the wavelength of the wave
1. Gap much wider than wavelength: little diffraction
2. Gap a bit wider than wavelength: diffraction at edges
3. Gap same as wavelength: maximum diffraction
Longitudinal waves
The vibrations are along the same direction as the wave transfers energy
e.g sound waves and ultrasound, shock waves
Transverse waves
The vibrations are at 90° to the direction energy is transferred by the wave
e.g Light and all EM waves, ripples on water
Describe the relationship between frequency and wavelength
The higher the frequency, the shorter the wavelength
Labe a transverse wave
do it
Wave equation
speed = frequency x wavelength
(m/s) (Hz) (m)
v = fλ
(speed of all EM waves are 3 x 10*8 m/s)
Draw diffraction of a wave as it
- passes an edge
- passes through a gap
draw it
What do waves transfer?
energy and not matter
What is the order of the EM spectrum in order of decreasing wavelength(increasing frequency)?
Radio, Microwave, Infrared, Visible, Ultraviolet, X-ray, Gamma
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What is the EM spectrum?
A continous range of electromagnetic waves
What are 2 characteristics of EM waves?
- transverse
- travel at the speed of light: 3 x 10 (*8) m/s
Give examples of the uses of EM waves
radio waves: broadcasting + communications
microwaves: cooking + satellite transmissions
infra-red: heaters and night vision
visible light: optical fibre + photography
ultraviolet: fluorescent lamps + killing bacteria in water purification
x-rays: observing the internal structure of objects + materials, medical application
gamma rays: sterilising food + medical equipment
What are the effects of these on the body: microwaves infrared uv X-rays gamma rays
what protects against this?
microwaves: internal heating of body tissue,
damaging cells if they overheat
infrared: skin burns,
skill cells are damaged by overexposure
uv: damage to surface cells and blindness,
can damage receptor cells in the retina
gamma: cancer, mutation
can cause cells to change arrangement
sunglasses / sun cream
What are analogue signals?
draw it
signals which can vary in frequency and amplitude
What are digital signals?
draw it
series of pulses consisting of 2 states, ON(1) and OFF(0)
Why are digital signals better than analogue?
As signals get transmitted, they become weaker and need to be amplified. Regeneration of digital signals create a clean, accurate copy of the original.
However regeneration of analogue signals also amplify any accompanied noise, which may create errors in the signal.
what is the relationship between frequency and time period?
frequency = 1 / time period
f = 1 / T
