Why can’t longitudinal waves be polarised?
Because there oscillations are parallel to the direction of wave travel
What does it mean if light is unpolarised?
The oscillations are random & not confined to any single plane
Explain how receivers are polarised?
They only receive oscillations in 1 direction & must be lined up in the same place to receive the maximum signal
What’s stress analyses?
- Different parts of the material reflecting light in different ways
- a polarised filter allows you to see the different levels of stress depending on the colours reflected
- it’s used to detect potential regions of weakness in a material
Explain how Polaroid sunglasses are used by fisher men
- unpolarised light from the sun is reflected by the sea
- the reflected light is mainly horizontally polarised
- polarising filter in the glasses cuts our horizontally polarised light
- light reflected from below the surface of the water is mainly vertically polarised & so passes through the polarising filter
How is shortsightedness fixed?
Shortsighted = rays focusing before the retina
Fixed with a concave lens (negative power)
How is longsightedness fixed?
Rays are focusing behind the retina
Fixed with a convex lens (positive power)
What’s absolute refractive index?
It’s how much a wave slows down as it moves from a vacuum in to the medium
What’s the midpoint go an oscillation called?
Equilibrium
Define oscillation
A repeated movement about a central position
What must a body have to be performing a simple harmonic motion?
- must have a restoring force acting upon it
- the magnitude of the force (the acceleration) is proportional to the displacement of the body from a fixed point
- the direction of the force (acceleration) is always towards that fixed point
Give 2 examples of a simple harmonic system?
A pendulum
Mass on a spring
What’s a radian?
Is the angle subtended at the center of a circle by an arc that’s equal to the length to the radius of the circle
How would you convert from degrees to radians?
x pi / 180
How would you convert from radians to degrees?
X 180 / pi
What’s phase difference?
- It’s the difference in angle between 2 identical waves that are out of step with each other
- when 2 waves have the same periodicity, so same frequency & travel at the same speed if they travel the same distance they’ll keep the same phase difference between
- but if one has to travel longer it comes out of phase
What’s path difference?
-it’s the difference (usually in terms of wavelength) between the lengths of 2 paths
What’s the phase difference of 2 objects that are oscillating in phase at the same each other (even if they have different amplitudes)?
O or 2 pi radians
What’s the phase difference of 2 objects that are exactly out of phase are 1/2 an oscillation apart?
Pi radians
