The path difference from the wave sources is and n is a natural number.
an 1 2bl
, where is their wavelength l
Waves A and B are out of phase and therefore have a path difference of along this line.
1 2
A crest from source A combines with a trough from source B, resulting in destructive interference.
Waves A and B have a path difference of 1 along this line.
1 2
AB Fig 10.14: Interference pattern illustrating waves’ sources that are out of phase INTERFERENCE PATTERN
An interference pattern is the pattern formed when waves from two (or more) coherent sources combine; it contains a repeating pattern of constructive and destructive interference.
It is an important fact that only a wave motion can undergo diffraction and interference. Both light and sound undergo these phenomena, proving that they are both waves.
DEMONSTRATION 10.1
Demonstration of Reflection, Refraction, Diffraction and Interference Using a Ripple Tank Apparatus
Ripple tank and accessories
Procedure Set up apparatus, the ripple tank, as shown in the photo. Demonstrate reflection using straight parallel waves. Place a barrier at an angle to the direction of propagation as illustrated in Fig 10.15(a).
Demonstrate refraction using straight parallel waves. Change the depth of the water in part of the tank as illustrated in Fig 10.15(b).
Demonstrate diffraction using straight parallel waves. Place a barrier with gap parallel to the wavefronts and vary the width of the gap as illustrated in Fig 10.15(c).
Demonstrate interference using two coherent wave sources as illustrated in Fig 10.15(d).
162 INVESTIGATING PHYSICS
Apparatus for the demonstration of wave phenomena using a ripple tank
