# Homework Help: 2 frequencies within an interference pattern

1. Feb 24, 2005

### lektor

Hi, short question.

What would be the effect of 2 sources both transmitting 2 different frequencies if placed in a way that forms an interference pattern.

ie. 2 aerials places parallel X meters apart transmitting in the same direction at 2 different frequencies per aerial.

Sorry if i didn't articulate this idea to well :<

2. Feb 24, 2005

### GCT

I would imagine that it would have no pattern or rather the pattern would be incomprehensible, useless. The main reason that for a monochromatic light is so that all of the miniscule changes and alterations in the light will be reflected in light going out of both slits. You should read up in your physics text, the beginning of the interferences chapter should explain these "miniscule" differences in more detail.

3. Feb 24, 2005

### BobG

You could do a poor quality simulation in Microsoft Excel that would at least give you the point.

Try this

Cell B1: (freq 1)
Cell C1: (freq 2)

A3: =1/(b1*10)
B3: =2pi()*b1
C3: =2pi()*c1

A5: 0
B5: =2*PI()/B1
C5: =2*PI()/C1
E5: =B5+C5

A6: =A5+$A$3
B6: =SIN((A6/$B$3)*2*PI())
C6: =SIN((A6/$C$3)*2*PI())
E6: =B6+C6

Copy Row 6 and paste into about the next 100 rows.

Chart A5 thru Column E of the last row you pasted.

You change the values in Cell B1 and C1 to change the frequencies of the two signals.
Column E is the sum of the two signals.

Mixing the signals obviously has an effect. Trying different frequencies, you visually see whether or not the pattern of the original signals are discernable or not. (since the number of cycles displayed is dependent on the first frequency, it's better if that's the lower frequency).

I'm not sure what the intent of your question is, at least in the context of whatever course you're taking, but in reality, whether or not the two signals 'interfere' with each other depends how close they are too each other and the receivers ability to discriminate the 'proper' frequency from the other.

4. Feb 24, 2005

### lektor

Im not sure if i phased my question correctly, sorry for the inconvenience.

I talked to my Physics teacher about it today and it seems that we haven't covered it yet, but he cleared it up for me :).

Btw, what type of chart should i use to for that? im interested to see how well this works :D

5. Feb 25, 2005

### BobG

You click on the chart icon and select a line chart, preferably without a bunch of boxes or x's for the data points. You'll see each original signal plus the sum of the signals.