RP1-Stationary waves on a string

• Equipment: signal generator, vibration generator, stand and counterweight, pulley, bridge, masses and mass holder, metre ruler, string, mass balance.
• Set up: Attach one end of string through the vibration generator to the stand and the other across the bridge over the pulley with a mass hanger hanging under gravity. Connect vibration generator to a signal generator and measure the distance between the vibration generator and bridge.
• Method: Place a fixed mass on the mass hanger and record. Adjust frequency of vibration generator until the string oscillates at the first harmonic. Change the length of the string and repeat, getting at least five different length results. Repeat the whole method at least two more times and calculate a mean.
• Graph: Plot a graph of frequency against 1/length of string. The gradient of the straight line equals half the wave speed and the line goes through the origin.
• Analysis: Wavelength equals 2 x length of string and therefore wave speed equals 2 x frequency x length of string. This is twice the gradient. The tension of the string equals the weight of the hanging mass and the mass per unit length of the string is the mass of the string divided by its full length.
• Safety: Stand could topple over - use a counterweight, masses could fall - place padding under them, string could snap - wear goggles.
• Alternative experiments: Since wave speed also equals root(tension/mass per unit length), varying the mass on the mass hanger or the type of string will affect the frequency required to reach the first harmonic.