# can waves of different frequencies

Discussion in 'MCAT Study Question Q&A' started by Bumbl3b33, Aug 8, 2011.

1. ### Bumbl3b33 Removed

Joined:
Feb 12, 2011
Messages:
530
1
Status:
Medical Student
cause destructive/construcive interference?

2. ### tn4596 5+ Year Member

Joined:
Jul 23, 2011
Messages:
845
10
Status:
Medical Student
Yes.
this result in beat. you will see a periodic contructive and destructive interference. the two wave have to be similar in frequency for this to happen. f(beat) = f (1) - f(2)

3. ### Sonyfan08 7+ Year Member

Joined:
Dec 4, 2008
Messages:
148
0
Status:
Pre-Medical
So, they have to have the same frequency for constructive/destructive interference to occur, right?

4. OP

### Bumbl3b33 Removed

Joined:
Feb 12, 2011
Messages:
530
1
Status:
Medical Student
apparently not....

5. ### costales 2+ Year Member

Joined:
Jul 25, 2011
Messages:
2,233
3,013
Status:
Resident [Any Field]
You get beats when two frequencies are about the same, but not exactly the same. So the answer is yes, they're different.

6. ### MD Odyssey 2+ Year Member

Joined:
Jun 26, 2010
Messages:
412
11
The perfect example of this is the signal received by an AM radio:

Notice that there are two waves which obviously have different frequencies that are superimposed to form the AM modulated signal on the bottom. It can be proven, with a lot of calculus, that any periodic function can be written as a sum of sines and cosines, each with a different frequency. This is the basic idea of something known as Fourier analysis. Here is a more complicated example of some sines and cosines added together to produce what looks like a square wave. You can imagine that, given an infinite number of sines and cosines, eventually you'll reproduce the original wave.

Stop hovering to collapse... Click to collapse... Hover to expand... Click to expand...
7. OP

### Bumbl3b33 Removed

Joined:
Feb 12, 2011
Messages:
530
1
Status:
Medical Student

AAMC #7 SPOILER, DON'T READ IF YOU HAVEN'T TAKEN IT

this is almost exactly what my question came from actually. The question asked, how come cell phones can recieve and transmit signals (a phone call) both at hte same time. and the answer said that because they're at different frequencies, they don't interfere with one another....care to shed light on this? I'm not sure if I fully understand based on what the above responses have been. I thought of beats too, that's why I eliminated that answer.

8. OP

### Bumbl3b33 Removed

Joined:
Feb 12, 2011
Messages:
530
1
Status:
Medical Student
bump?

9. ### costales 2+ Year Member

Joined:
Jul 25, 2011
Messages:
2,233
3,013
Status:
Resident [Any Field]
If two frequencies are far enough apart, there won't be superposition for interference. The limit is about 15 Hz, so if two sound waves are separated by more than 15 Hz, you will hear two different tones (no beats).

10. ### MD Odyssey 2+ Year Member

Joined:
Jun 26, 2010
Messages:
412
11
Two waves will always interfere, regardless of the frequency and phase difference. It may be more or less noticeable in certain cases, but it is always going to be there. The field at any point in space and time is ALWAYS due to the superposition of all the sources.

Stop hovering to collapse... Click to collapse... Hover to expand... Click to expand...

We’ve been on the Internet for over 20 years doing just one thing: providing career information for free or at cost. We do this because we believe that the health education process is too expensive and too competitive.

We believe that all students deserve the same access to high quality information. We believe that providing high quality career advice and information ensures that everyone, regardless of income or privilege, has a chance to achieve their dream of being a doctor.