1. For a standing wave to be set up in a string there has to be two waves travelling in it. Explain what has to be the same and what has to be different about the two waves.” (E) The waves must have the same frequency and amplitude but must be travelling in opposite directions. The waves must be travelling in opposite directions so that they can interfere to form a standing wave. If they were in the same direction, the result would be a travelling wave (i.e. not stationary) having the shape of the combined displacements. The waves must have the same frequency because if they didn’t the positions of constructive and destructive interference would not be fixed. The waves must have the same amplitude because if they didn’t, when they superpose with opposite phase they would not cancel out to make a node. Do now: Hātarei, 30 Kohi-tātea 2016

2. A 65cm long guitar string vibrates at its fundamental frequency of 456Hz. a)What is the wavelength of the vibration? b)Calculate the speed of the waves travelling down the guitar string? c)What is the frequency of the 4 th harmonic? Example: vibrating string

3. Figure 5.10 Practice drawing the modes and writing the formula for L or λ

4. Find the fundamental frequency and third harmonic of an organ pipe of length 50cm. Assume the organ pipe is closed at one end and the speed of sound in air is 330ms -1 Example: closed pipe