Waves Flashcards
What is a longitudinal wave?
A wave in which the direction of vibration of the particle is parallel to the direction in which the wave travels (propagates). Longitudinal waves have compressions and rarefactions.
What is a transverse wave?
A wave in which the direction of vibration of the particle is perpendicular to the direction in which the wave travels (propagates). Transverse waves have peaks and troughs.
Give 2 examples of longitudinal waves
Sound waves and primary seismic waves
Give 2 examples of transverse waves
Electromagnetic waves and vibrations in strings
What is polarisation?
Vibrations in on plane only
Can longitudinal waves be polarised?
No, only transverse waves can be polarised.
What is the displacement?
distance and direction from equilibrium position
What is the amplitude
maximum displacement of a vibrating particle.
What is the phase difference between two particles?
the fraction of a cycle between the two vibrations.
What is refraction?
When waves pass across a boundary between two mediums, they change speed and hence direction. When it enters a less dense substance, the speed increase and thus the wave refracts away from the normal.
What is diffraction?
the spreading out of waves when they pass through a gap or by an obstacle. The narrower the gap, the more the waves spread out.
What is superposition?
When waves pass through each other they combine, can be destructive or constructive.
What are stationary waves?
formed from two progressive waves. Have points of cancellation and reinforcement.
What are nodes?
points of no displacement
what are anti-nodes
points of maximum displacement
What is interference?
as waves pass through each other at constant frequency and constant phase difference, cancellation and reinforcement occurs at fixed positions.
What are coherent sources of waves?
same frequency with a constant phase difference.
Do freely vibrating stationary waves transfer energy?
no
What is the phase difference between two vibrating particles on a stationary wave?
zero- if the particles are separated by an even number of nodes. or adjacent nodes,
180 degrees- if the two particles are separated by an odd number of nodes.
Differences between stationary and progressive waves
for progressive waves, all particles vibrate at same frequency and same amplitude. for stationary waves, all particles except those at nodes vibrate at the same frequency. amplitude varies from zero at nodes to maximum at antinodes.
What does the pitch of a note correspond to?
frequency
Explain how an oscilloscope works
uses two pairs of deflecting plates, one horizontal and one vertical. electron is deflected by the plates which will alter its position on the screen. the displacement of the spot is proportional to the applied pd.
Why does refraction occur?
this is because the speed of the light waves is different in each substance.
What are the conditions for total internal reflection
the incident substance has a larger refractive index than the other substance.
the angle of incidence exceeds the critical angle
What happens when light diffracts through two slits?
alternate bright and dark fringes appear on the screen, they are the same width. fringes are evenly spaced and parallel to the double slits.
Why are dark and bright fringes formed in double slit interference?
light fringes occur when waves arrive in phase with each other. Where a dark fringe is formed, light arrives 180 degrees out of phase and so the two sources cancel each other out.
To measure the fringe separation, why would you measure across several fringes?
It reduces the percentage error in the readings.
Why are the double slits described as coherent sources?
they emit light waves of the same frequency with a constant phase difference.
how does laser light differ from non-laser light?
laser light is highly monochromatic
laser light is a source of coherent light
What is observed when light is diffracted by a single slit?
the central fringe is twice as wide as each of the outer fringes. The intensity of each fringe decreases with greater distance from the central fringe. The outer fringes are much less intense than the central fringe. Each of the outer fringes is the same width.
Why is light transmitted by a diffraction grating in certain directions only?
because the light passing through each slit is diffracted, the diffracted light waves from adjacent slits reinforce each other in certain directions only, and cancel out in all other directions.
