Wave I nterference Experiment

1. Wave Interference Experiment

2. Aim of the experiment “When pulses meet each other in the same medium, they can interact to form new pulses that can have greater or smaller amplitudes than the original pulses. This phenomenon is known as interference. In this experiment, you will use a ripple tank, filled with water. A vibrator is used to create single transverse pulses in the water and a pattern of interference will be observed.”

3. Superposition of pulses • When two pulses that are moving in the same medium, meet each other, they will interact with each other. • The interaction is known as superposition. • At the moment that the pulses overlap, they can strengthen each other and cause a greater amplitude, or they can weaken each other and cause a smaller amplitude. • The effect that two pulses have on each other when they are superimposed, is called interference.

4. ThePrinciple of Superposition Definition Types of Superposition When two pulses meet simultaneously at the same point in a medium, the instantaneous displacement at the point is the algebraic sum of the displacements of each pulse at that moment. • Two types of interference can take place: • Constructive interference • Destructive interference

5. Diagram of Constructive Interference Constructive Interference • When two pulses meet each other on the same side of the rest position, the result will be a greater amplitude. • After interference the pulses continue moving in their original direction of motion. An Example of Constructive wave formation

6. Diagram showing Constructive Interference b a b a a + b

7. Diagram of Destructive interference Destructive Interference • When two pulses meet each other on opposite sides of the rest position, the result will be a smaller amplitude. • After interference the pulses continue moving in their original direction of motion. Examples of Destructive Interference

8. Diagrams showing Destructive Interference a a a + (- b) - b - b

9. The Ripple Tank • A ripple tank consists of a tray that can be filled with water. • Vibrator beads are connected to a vibrator and can be used to produce single pulses in the water. • A piece of white paper is placed below the tray of the tank and a light source provides light from above. • An image of the interference pattern can be observed on the white paper.

10. Diagram of The Ripple Tank

11. Drawing of Interference in Ripple tank Constructive interference Destructive interference Note: Diagram must be drawn with solid and dotted lines to show difference between a crest and a trough

12. Wave Interference in nature

13. A Case Study Ships travelling the ocean sometimes suddenly and unexpectedly come face to face with a “wall of water.” This is called a rogue wave. Rogue waves may be more than 25 m high, which can be terrifying for the people on the ship. Many ships have been badly damaged or sunk by rogue waves, including the one in the movie made of Paul Gallico’s book called “The Poseidon Adventure”. Rogue waves are sometimes given as the reason for ships mysteriously disappearing, like the Australian ship the SS Waratah. On 26 July 1909 it left Durban harbour on the way to Cape Town with 211 passengers and crew on board. On 27 July several ships passed it. After that, it was never seen again. No wreckage from the ship or bodies were found. Scientists are still trying to figure out what causes rogue waves, but they believe in some cases they are the result of random superposition of waves that happen to meet at one place and time. From: Platinum Physical Sciences Learner’s book, grade 10 - 2011 The SS Waratah

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