Standing Waves

Superposition (a) explain and use the principle of superposition in simple applications (b) show an understanding of experiments that demonstrate stationary waves using microwaves, stretched strings and air columns (c) explain the formation of a stationary wave using a graphical method, and identify nodes and antinodes

Superposition waves/super.htm waves/super.htm

Experiments Over the next few lessons you will carry out experiments using strings and air columns. Make sure your notes are kept clear and up to date

Adding waves See p 140 in Physics for you. To graphically add any two waves – Draw the waves one below the other using the same x and y scales – Draw vertical lines through both waves at suitable points (peaks and troughs at least) – Draw a third graph by plotting the sum of the two displacements on the vertical line

Graphical formation of stationary waves For stationary waves you need to show this addition at several different times. Use time increments of T/4 This means that the phase difference changes by 90º in each diagram See p 142 in physics for you.

Diffraction (d) explain the meaning of the term diffraction (e) show an understanding of experiments that demonstrate diffraction including the diffraction of water waves in a ripple tank with both a wide gap and a narrow gap

Experiment The bending of waves as they pass through a gap or the edge of an object is called diffraction If you did not get to observe diffraction in the previous ripple tank experiment you will get another opportunity over the next few lessons.

_physics/kisalev/java/slitdiffr/index.html _physics/kisalev/java/slitdiffr/index.html Notes Sketch the general pattern Describe the effect of – Increasing wavelength – Decreasing slit width

Two source interference (f) show an understanding of the terms interference and coherence (g) show an understanding of experiments that demonstrate two-source interference using water, light and microwaves (h) show an understanding of the conditions required if two-source interference fringes are to be observed (i) recall and solve problems using the equation λ = ax /D for double-slit interference using light

Coherence Two waves are coherent if – They have the same wavelength – They have a constant phase difference It follows that if they are going to interfere (since they are the same type of wave in the same place) – They have the same speed – They have the same frequency

Experiments You have already observed two source interference in the ripple tank What was the effect on the distance between the minima, of increasing the wavelength (decreasing frequency)? What was the effect on the distance between the minima, of increasing the separation of the two sources What happened to the distance between the minima as you moved away from the source?

The equation The answers to the previous questions suggest that x= λD/s – Where – X = separation of minima (or maxima) – λ = wavelength – D is distance from the source – s = separation of sources

Diffraction gratings (j) recall and solve problems using the formula d sinθ = nλ and describe the use of a diffraction grating to determine the wavelength of light (the structure and use of the spectrometer are not included).