P11 Flashcards
What are progressive waves
Oscillation which travels through matter and transfers energy to particles in the medium
particle movement in a wave in medium
move from equilibrium position to new position then returned by restoring force
sound waves in air particles
air particles displaced and bounce of neighbours, those collisions provide restoring force
Difference between displacement time graph for longitudinal/ transverse
No fifference
phase difference
difference between position of particles on a wave
0/360/2π is in phase
180/π is antiphase
Reflection and refraction
reflection - both straight and circular, incidence = reflection angle
refraction - change direction either speed up and bend away with increase wavelength and vice versa (due to refractive index) - always some partial reflection too
speed of waves affected by depth of water - shallow slows down and shorter wavelength
Diffraction
When waves spread out after passing a gap or corner, occurs more when length of gap is similar to wavelength
Polarisation
Only in transverse waves, when particle oscillations are only in 1 plane
Partially occurs when reflecting off a surface - so more waves in a a particular plane but not completely
e.g light reflects off water and partially polarised horizontally
Intensity
radiant power passing through a surface per unit area
I = P/A (csa)
I is inversely proportional to d^2
more amplitude means more kinetic energy of particles as higher v in v^2 so intensity proportional to a^2
EM spectrum wavelengths
10^-1 boundary between radio and microwave
400 - 700nm visible
10^-13 to 10^-10 boundary between Xray and Gamma
Polarising filters and usage
Have slits in a particular orientation so only particles oscillating so can pass through
Used in eg aerials - some horizontal some vertical to prevent interference
refractive index
used to measure relative refractions
n = speed of light in vacuum/ speed of light in media
n of air is virtually 1, while e.g glass around 1.5
refraction law
n1 sin1 = n2 sin2
Total internal reflection
when a wave travels from a high refractive index to low refractive index and angle hitting is above critical angle all of light is reflected within the medium
how to work out critical angle from refractive index
sin C = 1/n
C = sin-1(1/n)
Experiment to find critical angle
Shine light into semicircle glass block at different angles until critical
shine onto centre of straight side to ensure 90 degrees measured
How much of a wave passes through a polarising filters
Can be calculated with sin/cos
