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Chapter 4 Waves (4.1 (Polarisation (Unpolarised light (If passed through 2…
Chapter 4 Waves
4.1
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Transverse
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EM Waves- vibrating electric field generates a vibrating magnetic field which generates a vibrating electric field further away etc
Polarisation
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Unpolarised light
If passed through 2 filters the light intensity will change unless the 2nd filter is perpendicular then no light will pass through
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Polaroid sunglasses- reduce the glare of light reflected by water or glass- the light is polarised reducing the intensity
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4.2
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Phase Difference
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Phase Difference- Fraction of a cycle between the vibrations of two particles measured in radians- 1 cycle is 2π radians
4.3
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Dish design
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Bigger dish= bigger signal can be received, more reflection of radiowaves
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4.4
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Waves in ripple tank
Two circular waves produced- cancellation= gaps in wavefronts and Reinforcement= where wavefronts shown
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4.6
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Stationary waves
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Can change pitch by altering length- more tension or shortening length increases pitch, less tension and more length lowers pitch
4.7
How to use
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To display a waveform
X-plates connected to oscilloscopes time base circuit- spot moves at constant speed left to right and then back faster- helps to calibrate
pd to be displayed is connected to y-plates so spot moves up and down as it moves left to right- this traces a waveform
Vertical displacement is proportionate to pd applied to y-plates so y-input is calibrated in volts per cm
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4.5
Stationary wave- created when 2 waves (equal amplitude and freq.) travelling in opposite directions meet- one is reflected and there is interference between them- i.e. by fixing both ends of string and making middle part vibrate so they reflect and pass through each other
Explanation
In general
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Node- No displacement or energy, Antinode- max displacement and energy
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Examples
Sound in a pipe- in a pipe closed at one end resonant freq. occur when there is an antinode at the open end and an node at the other
Using Microwaves
Microwaves from transmitter directed at a metal plate which reflects them back forming a stationary wave
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