2017_H2_Superposition_Lecture_Notes_(Teachers)

9646 H2 PHYSICS Lecture Notes Nanyang Junior College 1 Chapter 11 SUPERPOSITION Content Stationary waves Diffraction Interference Two-source interference patterns Diffraction grating Learning Outcomes Candidates should be able to: (a) explain and use the principle of superposition in simple applications. (b) show an understanding of the terms interference, coherence, phase difference and path difference. (c) show an understanding of experiments which demonstrate stationary waves using microwaves, stretched strings and air columns. (d) explain the formation of a stationary wave using a graphical method, and identify nodes and antinodes. (e) explain the meaning of the term diffraction. (f) show an understanding of experiments which demonstrate diffraction including the diffraction of water waves in a ripple tank with both a wide gap and a narrow gap. (g) show an understanding of experiments which demonstrate two-source interference using water waves, sound waves, light and microwaves. (h) show an understanding of the conditions required if two-source interference fringes are to be observed. (i) recall and use the equation λ =a x/D for double-slit interference using light. (j) recall and use the equation sinθ = λ / b to locate the position of the first minima for single slit diffraction. (k) recall and use the Rayleigh criterion θ ≈ λ / b for the resolving power of a single aperture. (l) recall and use the equation d sin θ = nλ to locate the positions of the principal maxima produced by a diffraction grating (m) describe the use of a diffraction grating to determine the wavelength of light (the structure and use of a spectrometer are not required). AND previously in the WAVES (chapter 10) syllabus: Candidates should be able to (n) Determine the wavelength of sound using stationary waves.

9646 H2 PHYSICS Lecture Notes Nanyang Junior College 2 1 PRINCIPLE OF SUPERPOSITION Previously in Waves, we were introduced to the wave model. In this chapter, we are studying the effect when more than one wave exist s simultaneously. Like how each pebble creates its own ripple in the wate r, what happens when two pebbles are thrown into the pond and the ripples spread out and overlap? When two waves meet, the resultant displacement is the vector sum of the displacements due to each individual wave. The figure below shows two wave pulses travelling in opposite directions. When the two waves meet, the resultant displacement of the rope is always equal to the sum of the displacements produced by each pulse. After the waves separate, they behave as if they had never met. Consider two transverse waves A and B emitted by two sources meeting and interfering at the point X. y t X Wave A Wave B Source A Source B

9646 H2 PHYSICS