# Homework Help: Determine if radio waves are constructive or destructive

1. Sep 26, 2011

### PCSL

I don't think I have to write out the problem but let me know.

There are two radio antennas emitting radio waves and a point was given to me to determine if constructive or destructive at that point.

I found the wavelength is 100m and the path difference is 200m. How can I determine if it is constructive or destructive??

edit: they are out of phase

Last edited: Sep 26, 2011
2. Sep 26, 2011

### PCSL

I'm going to bed soon and would lose if someone could help me out prior?

3. Sep 26, 2011

### SammyS

Staff Emeritus
Do you mean they are out of phase (by 180°) as they are transmitted at the radio antennas?

4. Sep 26, 2011

### PCSL

I would assume so but the problem does not say.

Here is the full problem:

Two out-of-phase radio antennas at x = +/- 300m on the x-axis are emitting 3MHz radio waves.Is the point (300,800) a point of maximum constructive interference, perfect destructive interference, or something in between?

It seems like this would be constructive but the answer is perfectly destructive and it makes no sense.

5. Sep 27, 2011

### SammyS

Staff Emeritus
If the antennas were in-phase, then there would be constructive interference.

6. Sep 27, 2011

### PCSL

It is out-of-phase though.