Standing Waves Superposition a explain and use the

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 • http: //www. acoustics. salford. ac. uk/feschools/ 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.

• http: //www. physics. uoguelph. ca/applets/Intr o_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).