Aim
Measure the frequency, wavelength and speed of waves by observing water waves in a ripple tank and waves on a stretched string or elastic cord.
Water Waves in a Ripple Tank
Equipment List
- Ripple tank
- Piece of white paper or card
- Suitable low voltage supply
- Motor (for moving a wooden rod in the ripple tank)
- Lamp
- Stopwatch
- Metre ruler
Method
- Fill the ripple tank so the water has a depth of approximately 5mm. Place the ripple tank on top of a piece of white paper or card.
- Place a wooden rod on the surface of the water and attach it to the low-voltage power supply and motor. Add a lamp to the circuit and hold the lamp above the ripple tank.
- View the wave pattern from the side of the tank, looking through the water.
- To measure the wavelength, place the metre ruler perpendicular to the wavefronts on the page. Measure across as many wavefronts as possible and divide by the number of waves.
- To measure the frequency, count the number of waves passing a particular point in the wave tank over a given time (measure 10 or 20 seconds using a stop clock).
- To calculate the wave speed, multiply the wavelength by the frequency.
Safety Precautions
- Take care when working with water and electricity in close contact.
Standing Wave on a Vibrating String
Equipment List
- Stopwatch
- Metre ruler
- Vibration generator
- 5W power signal generator
- Set of 100g masses and hanger
- Set of 10g masses and hanger
- Wooden bridge
- Pulley on a clamp
Method
- Produce a standing wave on the vibrating string by adjusting the frequency or the generator, the position of the wooden bridge and the tension in the string (by adding or removing masses). A standing wave is created when the wave doesn’t appear to move horizontally, instead the string appears to oscillate only vertically.
- To measure the wavelength, use a metre ruler to measure across multiple standing waves and divide by the number of total waves.
- To measure the frequency, use a stopwatch to time wave oscillations over ten complete cycles. If the wave is slow enough, time the point at the centre of the half-wavelength, starting at equilibrium and counting every other time the string passes the equilibrium as a complete cycle. Divide this value by 10 to find the time period.
Safety Precautions
- Don’t stand beneath weight stack
- Wear goggles and be cautious of the string snapping