2. Light Interference
• Mechanical waves with the same frequency
will interfere constructively in phase and
destructively out of phase
• We need to consider wavelength and relative
phase for experiments and calculations
• One way to observe is using a Michelson
interferometer
3. Michelson Interferometer
• Splits a beam of light, sends the two parts on
different paths of different lengths, which
causes a phase difference, then recombines
them
• It can measure tiny shifts in distance or wave
speed
4. Problem #1
• An experiment is taking place using a Michelson
interferometer
• It is within a vacuum chamber and a light of
wavelength 500 nm
• The experimenter wanted to determine the
bright outputs at different moved distances
• Find the output if he moves the mirror by 250 nm
• Then find how many times this output is reached
if the distance is misread and accidently moved 2
mm instead of 2 μm
6. Solution Part 1
• Moving the mirror at 250 nm would mean
that the path length would move double to
this
• This would mean that the path length would
move another full 500 nm
• We can conclude that the output would be
the same as we began with
7. Solution Part 2a
• The actual value of 2 μm the mirror was
supposed to moved would mean the path
length change is 4 μm
• The accidental value of 2 mm the mirror was
actually moved would mean the path length
change is 4 mm
8. Solution Part 2b
• We can find how many times the output of
500 nm was reached by dividing the change in
path length by this value
• Original: 4*10-6/500*10-9 = 8
• Accidental: 4*10-3/500*10-9 = 8000
• 8000/8 = 1000 times off
• This slight mistake caused the experimenter to
make a huge miscalculation
