# What is a wavefront? sine or cosine graph?

What is a wavefront? Huygen's principle says that every point on a wavefront acts as a source of wave with the same speed. Now I am not asking you what that means, but i don't understand what a wavefront is. Is that like a circle? But wave is usually like a sine or cosine graph, so what's the relations between them. thanks.

mgb_phys
Homework Helper
Think of each individual wave as looking like a sin curve.
A wavefront is a set of waves side by side.
Consider a boat going up and down in a harbour it makes individual waves that all travel out at the same speed, the wavefront is the perimeter of this expanding 'front' of waves.
Huygens principle says that when you are considering how any of the waves on the wavefront interact with anything else you don;t have to wory about how they were created or got there - you can think of the source of each wave beign on the wavefront.

learningphysics
Homework Helper
What is a wavefront? Huygen's principle says that every point on a wavefront acts as a source of wave with the same speed. Now I am not asking you what that means, but i don't understand what a wavefront is. Is that like a circle? But wave is usually like a sine or cosine graph, so what's the relations between them. thanks.

Yes, if you drop a pebble in a pond... you get waves diverging out from the place where you drop the pebble... in all directions... or you can think of it as one 3-dimensional wave. If you connect the points that have the same phase, you'll get a circle in this case... that circle is a wavefront... In other cases the wavefront won't be a circle... sometimes it will be a sphere... for example light propagating from a point source... It's basically the surface you get when you connect points of the same phase...

Think of each individual wave as looking like a sin curve.
A wavefront is a set of waves side by side.
Consider a boat going up and down in a harbour it makes individual waves that all travel out at the same speed, the wavefront is the perimeter of this expanding 'front' of waves.
Huygens principle says that when you are considering how any of the waves on the wavefront interact with anything else you don;t have to wory about how they were created or got there - you can think of the source of each wave beign on the wavefront.

What do you mean by expanding 'front' of waves? What does 'front' mean here? If I imagine that individual wave is like a sine curve, then they sort of connect together side by side and form a circle? That's the wavefront?

mgb_phys
Homework Helper
Yes exactly, although it's only a circle for waves coming from a point.

Do you know what a spherical wave is? Because in my book, when it talks about wavefront, it then also talks about spherical wave. So i dont know if they have any relations.

Do you know what a spherical wave is?

they are the one that are produced in water when you drop a stone in the water.

they have wavefronts but those wavefronts are circular.

lightgrav
Homework Helper
the FRONT of a wave is the place
where the material is (first) disturbed
away from its equilibrium situation.
The disturbance ALWAYS propagates
perpendicular to the wave front.

*circular* wave fronts are 1-dimensional arcs
that move outward and cover a 2-d surface
. . . like water wave ripples.

*spherical* wave fronts are 2-d shells
in a 3-d volume ... sound from a hand-clap, for example.

they are the one that are produced in water when you drop a stone in the water.

they have wavefronts but those wavefronts are circular.

but are waves supposed to look like a sine or cosine curve, which is not like circular wave produced by dropping stone in water? Since when I interpret "spherical wave" literally, I imagine its shape is llike circular. Or you mean only wavefronts are circular not the wave itself? I get confused with how wave and wavefronts should look like.

the FRONT of a wave is the place
where the material is (first) disturbed
away from its equilibrium situation.
The disturbance ALWAYS propagates
perpendicular to the wave front.

*circular* wave fronts are 1-dimensional arcs
that move outward and cover a 2-d surface
. . . like water wave ripples.

*spherical* wave fronts are 2-d shells
in a 3-d volume ... sound from a hand-clap, for example.

What do you mean by 1-dimensional? a line? wavefront is a part of wave?

What do you mean by 1-dimensional? a line?

A ray (As those things can't move back and forth )..they just move in one direction.