# Wavefront

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#1
Can someone please explain the definition of wavefronts? And also spherical wavefronts in relation to refraction?
These two terms really confuse me so if someone can break it down will be amazing!!
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1 year ago
#2
It's all a bit subtle, trying to describe complex physics with words!

I think its also related to the wave/particle identity, or wavicle as I call it

QM Wave–particle duality - lots of interesting reading

This isn't a definition, it is how I understand it
if you imagine a point source (isotropic) emitter ( a tiny radio station that beams Classic FM on shortwave from a nano antenna - with equal power radiated equally in all directions)

then at the moment of transmission of Beethoven's 5th Symphony, the Di DI Di Dah start, that first "Di" will generate a bubble of shortwave sinusoidal radiation out into the ether, aether, space.

That first D, of Di, is the wavefront, the leading edge of a wave that wasn't there, but now is there.

it is a spherical wavefront due to the characteristics of the emitter - isotropic idealistic - bubble

there must be some animation on You Tube of two bubbles interfering - perhaps through a slit , diffraction grating or two, although that wave through duality is also a wavicle, particle (any sentence with the word Quantum in it is inherently wrong, including this one, hence why I just used QM earlier)
if we then re-position our brain to consider the linear sinusoidal instead, taking a crosswise slice through the bubble, then you can see how this wave can be refracted through a medium of different density/different local speed of light etc

1 -| ,-'''-.
| ,-' `-.
| ,' `.
| ,' `.
| / \
|/ \
----+------------------\--------------------------
| \ /
| pi/2 pi \ 3pi/2 / 2pi
| `. ,'
| `. ,'
| `-. ,-'
-1 -| `-,,,-'

Qualifications: I are engineer, but I did some of my engineering with nobel prize winners in physics in the depths of an antiproton collider,
hopefully a -real- fizzycist will put you right, my answer is just an approximation - but I did use this "refraction" to sample the beam by inserting a wedge of engineering bakelite-is stuff, coupling a transcendental wave of a dielectric layer, from a bunch of particles

(sorry if the ASCII is melted by fonts or TSR, yep - they can't cope with the spaces)
0
1 year ago
#3
(Original post by Helloaaa)
...
Think of a distant source emitting EM waves, incident on a large sheet at 90° to direction of wave travel. All waves will strike this sheet at e.g) max amplitude (or pick any other point in a wave cycle).

This sheet, a surface at 90° to wave travel, represents a wavefront - all waves are incident with equal phase. Imagine the sheet moving at speed c, representing these corresponding points of equal phase moving through time - wavefronts do this.

The above relates to plane waves (travel in parallel along an axis, striking a sheet on the perpendicular axis). Spherical wavefronts can occur in e.g) a point source, where radiation propagates with equal power in all directions (uniform). Again, wavefronts 90° to direction of wave travel (surface tangent vs radius).

RE: refraction, this occurs when 1 part of a wavefront enters a medium (of higher/lower index) before other parts do, changing its speed & phase (before other parts have), resulting in a change of direction.
Last edited by Physics Enemy; 1 year ago
0
4 months ago
#4
(Original post by Helloaaa)
Can someone please explain the definition of wavefronts? And also spherical wavefronts in relation to refraction?
These two terms really confuse me so if someone can break it down will be amazing!!
Definition: The locus of points on a wave that are in phase with each other.

Explanation of definition:
Locus means the shape (point, line, surface or volume etc.), typically matching some criteria.
Locus of points means the locus formed by a set of points matching some criteria.
points: refers to a point in space which may have something there that can oscillate e.g. particle(s) or field(s)
in phase: points are in phase when their disturbance/displacement from their equilibrium position oscillate 'in time' with each other. i.e. they are all troughs at the same time and then all peaks together (half a time period later).
disturbance/displacement: could be the distance a particle moves (as with sound) from its equilibrium position or it could be the electric field strength (and direction) (as with EM-waves). Note that displacement used here overlaps with significantly but not completely with displacement that you learn about in suvat.

There are unclear definitions given by educational sources online, but if you search up about 6 of them, you can start to build a picture. Source: I am a physics teacher of 4 years, tutor of >10 years and scored 98% in my A-level physics having self taught it. To answer this question I reviewed 10 definitions online and evaluated them against each other for accuracy and clarity and then made my own hybrid definition.

Spherical wavefront is a wavefront that has the locus (shape) of the surface of a sphere (not a solid sphere). A sphere is a locus of points that all have the same distance from one point (in this case the source of the wave).
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