# B Michaelson-Morley experiment

1. Oct 12, 2016

### LSMOG

In Michaelson-Morley experiment, how woul we know if there was a difference in speeds of reflected beam. Please, Im lost.

2. Oct 12, 2016

### Ibix

The beams would take different times to get to the output arm, so would be out of phase. You would see a different fringe pattern as a result.

3. Oct 12, 2016

### Simon Bridge

... you would know because of the interference pattern.
What level of education are you at?

4. Oct 12, 2016

### LSMOG

Its B level, I made a mistake to choose A level.
I thought the interference patterns tells us about the phase shift of the waves, I didn, know if it has anything to do with velocities. Am I correct?

5. Oct 12, 2016

### Ibix

You get a phase difference because of the different wave speeds. Think of the wave crests travelling through the two arms. If the speed of light is different then two wave crests leaving the beam splitter at the same time take different amounts of time to travel the same distance, so return at different times. That means there's a phase difference which depends on the difference in speeds along the two arms.

Actually, there is no phase difference and we have to develop relativity to explain that. But if there were a speed difference, the above is how an interferometer would detect it.

6. Oct 12, 2016

### Simon Bridge

I'll leave Ibix to puzzle it out - check in in the morning (local time).
What does "B level" mean? To me "A level" was a UK exam for secondary school.
For "education level" please reply with highest education achieved - ie: secondary (high school) or tertiary (college) and what year (1st year, 2nd year etc).
For instance: Michealson-Morely experiment may be encountered, in NZ, in senior secondary school (year 11 or 12, ie 16-18yo) or in the 1st 2 years of University.
I'm puzzled because you have asked, in another thread, about how things get to have a colour - which would normally be covered, in NZ, in year 8 or 9 science classes (ie 13-14 yo students).

7. Oct 12, 2016

### Staff: Mentor

This refers to the PF thread levels. We allow the OP to specify the level of response that they would like in order to help us respond at a helpful level.

B level is "basic" it means that the OP is looking for answers at a pre-college level. Either no math or only algebra.

I level is "intermediate" it means that the OP is looking for answers at an undergraduate college level. Some simple calculus would be appropriate.

A level is "advanced" it means that the OP is looking for answers at a post-graduate college level. All advanced math is appropriate.

8. Oct 12, 2016