Water Waves Ripple tank experiment Basic set-up for the ripple tank experiment Next Slide Mechanism of producing bright and dark fringes Stroboscope : freeze the wave pattern Photo Experimental precautions Diagram Photo Explanation Set-up

Water Waves Wavefronts and rays Straight wavefronts and circular wavefronts Next Slide Rays : the direction of travel of the wavefronts Diagram Wavefronts

Water Waves Reflection of waves Reflection of water waves by a straight barrier Next Slide Reflection of water waves by curved barriers Photo Effects of reflection on frequency, wavelength and speed Diagram Wave Phenomena 1

Water Waves Refraction of waves Method of creating different media for water waves Next Slide Refraction of water waves Diagram Photo Effects of reflection on frequency, wavelength and speed Diagram Wave Phenomena 2

Water Waves Diffraction of waves Diffraction of water waves at different kinds of barriers Next Slide Photo Effects of diffraction on frequency, wavelength and speed Diagram Wave Phenomena 3

Water Waves Interference of waves Conditions for setting up interference Next Slide Photo Interference pattern of water waves Photo Constructive interference, destructive interference and path difference Diagram Nodal lines and anti-nodal lines Diagram Wave Phenomena 4

END of Wave Phenomena

Water Waves Click Back to A ripple tank experimental set-up is shown below : Back to Set-up

Water Waves Next Slide The light source (lamp of projector) is placed below the transparent ripple tank. The waves on the water surface become convex and concave lenses which converge and diverge the light. Convergent light rays form bright fringes on the screen. Set-up

Water Waves Click Back to Back to bright fringes screen Set-up

Water Waves Click Back to Two stroboscopes are shown below : Back to Set-up

Water Waves Click Back to Cotton is placed at the boundary of the ripple tank to reduce reflection of water wave. Vibration of the motor creates the water wave. Back to Set-up

Water Waves Click Back to Straight wavefonts and circular wavefonts are shown below : Back to Wavefronts

Water Waves Click Back to Back to raywavefrontsource straight wavefront circular wavefront Wavefronts

Water Waves Click Back to Back to Reflection of straight wavefront by a straight barrier is shown below : Wave Phenomena 1

Water Waves Click Back to Reflection of water wave by a curved barrier is shown below : Back to Wave Phenomena 1

Water Waves Click Back to Reflected water wave has no change in frequency, wavelength and speed Back to The rays of the incident wave and reflected wave obey the law of reflection in optics. Wave Phenomena 1

Water Waves Click Back to A piece of glass is placed in the ripple tank so that two regions with different depth are created. Back to region Aregion B glass block Wave Phenomena 2

Water Waves Click Back to Water wave travels from region A to region B (top-view) : Back to region B region A Wave Phenomena 2

Water Waves Next Slide Water wave has a smaller speed and wavelength in the shallow region. However, the frequency remains constant. region Aregion B glass block less dense medium (fast region) denser medium (slow region) > 2 Wave Phenomena 2

Water Waves Click Back to Therefore, region A is considered as a less dense medium and B as a denser medium. Refraction happens when the wave enters a different medium. Back to Less dense medium  Denser medium (Ray bent towards normal) Denser medium  Less dense medium (Ray bent away from normal) region B region A region B region A Wave Phenomena 2

Water Waves Next Slide Diffraction happens when water wave encounters an opening on a barrier as shown below : Small spread of wave at the boundary of the straight wavefront. ( << size of the opening) Wave Phenomena 3

Water Waves Next Slide Spread of wave is so serious that the straight wavefronts have been changed to semi-circular wavefronts. (  size of the opening) Wave Phenomena 3

Water Waves Click Back to Spread of wave can also be observed as we place a barrier in front of the wave. << the size of the barrier  the size of the barrier Back to Wave Phenomena 3

Water Waves Click Back to Since there is no change of medium, the frequency, wavelength and speed of the water wave remain constant. Back to Wave Phenomena 3

Water Waves Next Slide In order to produce the interference pattern of waves, we need two sources of circular water waves with the following requirements : 1. The separation of the sources should not be larger than several wavelength of the wave used. 2. The sources should vibrate up and down exactly at the same pace. (They are in phase.) 3. The sources should be of the same frequency. (That means the waves produced by the sources would be of the same frequency, wavelength, speed and amplitude.) Wave Phenomena 4

Water Waves Click Back to The following set-up is used to produce the interference pattern : Back to Wave Phenomena 4

Water Waves Click Back to The interference pattern produced is shown below : Back to Wave Phenomena 4

Water Waves Next Slide Constructive Interference : crest + crest (A) or trough + trough (B) Destructive Interference : crest + trough (C and D) S1S1 S2S2 At certain instant, A B C D Wave Phenomena 4

Water Waves Next Slide Constructive Interference Destructive Interference S1S1 S2S2 Point at which the waves meet S2S2 S1S1 Point at which the waves meet resultant amplitude Wave Phenomena 4

Water Waves Click Back to We can consider the path difference to determine whether a point has constructive or destructive interference Path difference : PS 1  PS 2 Constructive interference : PS 1  PS 2 = m Destructive interference : PS 1  PS 2 = (m + 1/2) Back to m is a integer (m = 0, 1, 2, ) Wave Phenomena 4

Water Waves Next Slide We join all constructive interference points with same value in path difference together to get the antinodal lines. We join all destructive interference points with same value in path difference together to get the nodal lines. S1S1 S2S Wave Phenomena 4

Water Waves Next Slide As frequency increases (wavelength decreases), the separation between the nodal lines and the antinodal lines decreases. As the separation of the sources decreases, the separation between the nodal lines and the antinodal lines increases. Wave Phenomena 4

Water Waves Next Slide Wave Phenomena 4

Water Waves Click Back to Back to Wave Phenomena 4