# Phase difference of original and reflected wave

1. Aug 8, 2014

### somecelxis

1. The problem statement, all variables and given/known data
A radio station transmits a radio wave of 100Mhz. The radio wave is detected by a receiver via two diffrent paths , a direct path and refelcted path form a wall. The distance travelled by the radio wave for a direct path and refelcted path is 1500m and 1512 m respectively. Explain whether the intefrenece is constructive od destructive?

2. Relevant equations

3. The attempt at a solution
refer to the sample ans attcahed, i don't undertstand why there's a phase change of 1/2 lambda when the wave is reflected?

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2. Aug 8, 2014

### Staff: Mentor

It is a characteristic of waves. Remember the wave travelling down a rope until it reaches the end anchored to a wall? When the wave hits the wall it returns along the rope, but inverted. Inversion of a sinewave = 180 degree shift

The dark bands in a soap bubble are explained based on this inversion when reflecting off a more optically dense medium. When reflected off a less dense medium there is no inversion.

Last edited: Aug 8, 2014
3. Aug 8, 2014

### Vibhor

Hello Nascent

Does the phase change of reflected wave depend on the type of waves we are dealing with ?

If instead of radio wave ,the question had sound wave reflecting from the wall , do you think it would also undergo phase change of 180 degrees ?

Thanks

4. Aug 8, 2014

### somecelxis

hi, i have attched some of the standing wave pattern at difefrent time. for time T= t/4 , yes, the phase difference is 180 degree shift , but when t=0 . there's no phase difference for the incident and reflected waves.

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5. Aug 8, 2014