# Calculating phase difference

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How would you work out phase difference between two points given the frequency, distance and wavelength...and how would you express this in radians.

EG:

Wavelength of a wave is 1.2m, Speed is 3.6ms-1,distance between two points P and Q is 0.4m

What is the phase difference....

The mark scheme says 2(pi)/3.....how did they get that??

Any help will be appreciated

Thanks in advance

EG:

Wavelength of a wave is 1.2m, Speed is 3.6ms-1,distance between two points P and Q is 0.4m

What is the phase difference....

The mark scheme says 2(pi)/3.....how did they get that??

Any help will be appreciated

Thanks in advance

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#2

(Original post by

How would you work out phase difference between two points given the frequency, distance and wavelength...and how would you express this in radians.

EG:

Wavelength of a wave is 1.2m, Speed is 3.6ms-1,distance between two points P and Q is 0.4m

What is the phase difference....

The mark scheme says 2(pi)/3.....how did they get that??

Any help will be appreciated

Thanks in advance

**Zwitter Ion**)How would you work out phase difference between two points given the frequency, distance and wavelength...and how would you express this in radians.

EG:

Wavelength of a wave is 1.2m, Speed is 3.6ms-1,distance between two points P and Q is 0.4m

What is the phase difference....

The mark scheme says 2(pi)/3.....how did they get that??

Any help will be appreciated

Thanks in advance

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#3

phase difference = 2pi x path difference divided by lambda

path difference is like (n + 1/2)lambda etc..

path difference is like (n + 1/2)lambda etc..

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#4

so path difference = 1/3 lambda and thus the two lambda's in the equation cancel out leaving phase difference = 2pi x (1/3) = 2pi/3

that gives you the answer

that gives you the answer

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So am i right in saying that a general formula to calculate phase difference is:

distance travelled/wavelength x 2(pi) ???

distance travelled/wavelength x 2(pi) ???

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#6

not distance travelled, but the difference in the distance between the two points in terms on lambda, i.e.a multiple or fraction of the wavelength

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#8

i came across a question with the same information:1. they've given a displacement/distance graph with a straight line running through the x axis saying its a stationary wave at t=0.

2. then they say it has a period of 20ms and wavelength 1.2m. max amplitude is 5mm

they ask what is the phase diff between particles of the string at .4m and .8m.

the MS says 180 degrees/ pi radians

can someone explain this to me?

2. then they say it has a period of 20ms and wavelength 1.2m. max amplitude is 5mm

they ask what is the phase diff between particles of the string at .4m and .8m.

the MS says 180 degrees/ pi radians

can someone explain this to me?

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#9

(Original post by

i came across a question with the same information:1. they've given a displacement/distance graph with a straight line running through the x axis saying its a stationary wave at t=0.

2. then they say it has a period of 20ms and wavelength 1.2m. max amplitude is 5mm

they ask what is the phase diff between particles of the string at .4m and .8m.

the MS says 180 degrees/ pi radians

can someone explain this to me?

**Amirtha**)i came across a question with the same information:1. they've given a displacement/distance graph with a straight line running through the x axis saying its a stationary wave at t=0.

2. then they say it has a period of 20ms and wavelength 1.2m. max amplitude is 5mm

they ask what is the phase diff between particles of the string at .4m and .8m.

the MS says 180 degrees/ pi radians

can someone explain this to me?

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#10

(Original post by

Not sure entirely about the nature of the question - straight line displacement as a function of distance doesn't look like a wave but assuming the statement that we're looking at a stationary wave applies, we can draw certain conclusions. A stationary wave with a node at x = 0 and wavelength 1.2m will have nodes at x = 0.6 m, 1.2 m, 1.8 m etc. Points either side of a node will oscillate out of phase with each other, so the phase difference between them will be pi radians or 180 degree. This is true for any points either side of a node. Points at x = 0.4m and x = 0.8m are equal distances from the 0.6 m node so they will oscillate out of phase with each other with equal amplitude to each other.

**astro67**)Not sure entirely about the nature of the question - straight line displacement as a function of distance doesn't look like a wave but assuming the statement that we're looking at a stationary wave applies, we can draw certain conclusions. A stationary wave with a node at x = 0 and wavelength 1.2m will have nodes at x = 0.6 m, 1.2 m, 1.8 m etc. Points either side of a node will oscillate out of phase with each other, so the phase difference between them will be pi radians or 180 degree. This is true for any points either side of a node. Points at x = 0.4m and x = 0.8m are equal distances from the 0.6 m node so they will oscillate out of phase with each other with equal amplitude to each other.

and what if the points are not of equal distance from the node, what will be the phase difference? like between .5m and .8m?

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#11

(Original post by

i thought points either side of a node oscillate in phase. how is it not in phase?

and what if the points are not of equal distance from the node, what will be the phase difference? like between .5m and .8m?

**Amirtha**)i thought points either side of a node oscillate in phase. how is it not in phase?

and what if the points are not of equal distance from the node, what will be the phase difference? like between .5m and .8m?

The motion of a point at distance x along a stationary wave can be described by A*sin(2*pi*x/lambda)*sin(omega*t). For a given value of x (i.e. a fixed point on the string), the motion is sinusoidal with time, with amplitude given by A*sin(2*pi*x/lambda). All the points between consecutive nodes are moving in phase with each other. For 0<x<(lambda/2), the amplitude is positive. For x = (any integer)*(lambda/2), then the amplitude is zero and we have a node. For (lambda/2)<x<lambda, the amplitude is negative and the string travels in the opposite direction, corresponding to a phase shift of pi relative to points on the string either side of the nodes.

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#12

0.4 divided by the wavelength (1.2) so you get the phase difference. To get that answer in radian multiply it by 2 pi.

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#13

The formula for phase difference = K • delta x Since k = 2 pie / lemda Substituting the value of lemda = 1.2 We get k = 2 pie / 1.2 ,And delta x = 0.4 Hence solving , k • delta x , We get the answer 2 pie / 3

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