Required Practical 1 - Stationary Waves

List the equipment needed for required practical 1.

Signal generator

Stand

Pulley

Wooden bridge

100g masses and holder

Meter rule

String

Balance

Describe a simple method to investigate how the frequency of waves on a string varies with length.

1. set up the apparatus as in the diagram

2. Adjust l so it is 1m (using meter rule)

3. Increase f until it oscillates in the first harmonic and record f 

4. Repeat reducing the length by 0.1m each time

5. Repeat 2x and find a mean f for each l

6. Measure and record the mass of the string

What graph should be plotted for required practical 1?

f against 1/l

Describe how to find wave speed from the graph of f against 1/l

wavelength = 2 x length

speed = 2 x frequency x length = 2 x frequency / 1/length = 2 x gradient

Describe how to use the value of v obtained from the graph to find the experimental error.

Use the mass per unit length (found using the mass of the string) and use the equation v = (root) tension / mass per unit length

State one safety precaution when carrying out required practical 1.

Use a counterweight to stop the stand from toppling over

What improvements can be made to help the validity of the experiment?

Repeat with different masses to change the tension or different thicknesses to investigate changes in these parameters

Use an oscilloscope to confirm the signal generator’s readings

Leave the generator for 20 mins between readings to stabilise