Imaging and signalling Flashcards
How is information transferred?
Waves
How does medical scanning use waves?
Ultrasounds scans build up an image of a foetus by detecting reflected ultrasound waves
What is a progressive wave?
A wave that carries energy (and usually information) from one place to another without transferring any material
How can you tell a wave carries energy?
EM waves cause things to heat up
X-rays and gamma rays knock electrons out of their orbits causing ionisation
Sound waves make things vibrate
What happens to the source of waves?
Loses energy as the waves are carrying energy
What is the displacement of a wave?
How far a point on the wave has moved from its undisturbed position
What is the amplitude of a wave?
The max. displacement of a wave from its undisturbed position
What is wavelength?
The length of a whole wave (distance from one point on a wave to its identical point on the adjacent wave)
What is the period of a wave?
The time taken for a whole vibration
What is frequency?
The no. of waves passing a given point per second
What is phase difference and what is it measured in?
The amount by which one wave lags behind another wave
degrees or radians
What is the wave equation?
v=fλ
What are electromagnetic waves?
Transverse waves which consist of two perpendicular planes, a magnetic and an electric field
What is a transverse wave?
A wave where the vibration is at right angles to the wave’s direction of travel
What is a longitudinal wave?
A wave where the vibrations are along the wave’s direction of travel
What is intensity?
The rate of flow of energy per unit area at right angles to the direction of travel of the wave
(measure of how much energy a wave is carrying)
Intensity equation (waves) and unit?
intensity = power/area
Wm-2
What is a polarised wave?
A wave that only oscillates in one direction
What do all electromagnetic waves have in common?
Transverse waves
Can be polarised
Travel at the speed of light in a vacuum
What is a polarising filter?
Something that only transmits waves oscillating in one direction
What happens when you shine light through two polarising filters at right angles?
No light will be transmitted as all directions of oscillation will be blocked
How do you know if a wave is transverse?
If it can be polarised
What happens when two polarising filters are at 45°?
Intensity getting through the second filter will be exactly half of that transmitted through the first
What are some examples of polarising filters?
3D filed use polarised light to create depth, the filters in each lens are at right angles to each other so each eye gets a slightly different picture
polaroid sunglasses use polarising filter to help prevent glare