PHASE & PHASE DIFFERENCEPHYS 101 LEARNING OBJECTS

PHASE ( )

• corresponds to the position and time on the wave function

• based on the above example of a wave function, points 1, 2, 3, 4 and 5 can be referred as 0, pi/2, pi, 3pi/2 and 2pi when thinking in respect of the phase of this wave

• labelling of 0, pi/2, pi, 3pi/2 and 2pi are arbitrary may be labelled along different points of wave (as long as its indicates accurate position of wave at specific time)

PHASE DIFFERENCE

• “difference between the phase at 2 points, at the same time”

• when blue wave is at pi/2, red wave is at 0 phase ; when blue wave is at pi, red wave is at pi/2 phase (etc.)

• can describe this offset between 2 waves as the phase difference

• in this case: difference of pi/2 in the phase

• the blue wave is always to the left of the red wave by pi/2

• if these waves are traveling to the left, blue wave is leading red wave by pi/2 of phase

• if waves traveling to the right, blue wave is trailing from the red wave by pi/2 of phase

EQUATION FOR THE PHASE DIFFERENCE IN HARMONIC WAVES

PHASE DIFFERENCES FOR A PERIODIC WAVE

• for a periodic wave, the difference in phase is set due to its periodic nature

• the following table will be useful when determining phase difference of periodic wave:

IN PHASE / OUT OF PHASE

• In phase

• when 2 points on a wave that are an integer (full number) multiple of wavelength apart from each other and have a phase difference of 2pi

• points have equal displacements at ALL TIMES

• Out of phase

• 2 phase that are an odd half-integer multiple (1/2, 3/2, 5/2…) of a wavelength apart are pi rad out of phase with each other

• points ALWAYS have equal and opposite displacements from equilibrium