# aqa a level physics required practicals

equipment, method, diagram, information, risks, evaluations, graph, uncertainties of all the first 6 practical's required at AS level for teaching from September 2015

Teacher recommended

- Created by: tomaustin99
- Created on: 03-06-16 14:44

First 433 words of the document:

Required practical's AQA ALevel Physics September 2015

Frequency of a stationary wave

Equipment

Signal generator

Vibration generator

Stand

2kg mass

1.5m length of string (eg 1.5mm thick)

Pulley which can be clamped to the bench

Wooden bridge slightly higher than the pulley

100g masses on a holder

Metre ruler

An electronic top pan balance with precision 0.1g or better

Method

1. Set up the apparatus as shown in the diagram.

2. Adjust the position of the bridge so that l is 1.000m measured using the metre ruler.

3. Increase the frequency of the signal generator from zero until the string resonates at its

fundamental frequency (as indicated in the diagram with a node at each end and a central

antinode).

4. Read the frequency f, on the signal generator dial.

5. Repeat the procedure with l = 0.900, 0.800, 0.700, 0.600 and 0.500m.

6. Obtain a second set of results by repeating the experiment and find the mean value of f

for each value of l.

7. Plot a graph of mean 1/f against l.

8. Draw the best straight line of fit though the points and find the gradient (the graph should

be a straight line through the origin).

9. The speed of the travelling waves on the string is c = f where is the wavelength.

When the string is vibrating in its fundamental mode, = 2l. Hence c = 2fl. The gradient

is 1/ fl so c is given by 2/gradient in ms1.

10. The speed is also given by c = (T/m) where T is the tension in the string in N and m is the

mass per unit length of the string in kgm1

11. With a 100g mass hanging from the string, T = 0.981N. m can be found by weighing the

1.5m length of string on an electronic balance, converting this into kg, and dividing by 1.5.

These values can then be substituted into the above equation to find another value for c,

which can be compared to the value obtained from the graph.

12. The experiment can be repeated with different masses hanging from the string, and

different thicknesses of string to investigate the effect of changing T and m.

13. Doubling the fundamental frequency while keeping l, T and m constant will cause the

string to resonate in its second harmonic (or first overtone, with nodes at either end, a

central node, and two antinodes). Tripling the frequency will give the third harmonic, and

so on

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