Required Practical 1 Flashcards

(9 cards)

1
Q

What is the aim of RP1?

A

The overall aim of the experiment is to measure how the frequency of the first harmonic is affected by changing one of the following variables:

The length of the string

The tension in the string

Strings with different values of mass per unit length

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2
Q

Variables

A

Independent variable = either length, tension, or mass per unit length

Dependent variable = frequency of the first harmonic

Control variables

If length is varied = same masses attached (tension), same string (mass per unit length)

If tension is varied = same length of the string, same string (mass per unit length)

If mass per unit length is varied = same masses attached (tension), same length of the string

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3
Q

Equipment resolution

A

Resolution of measuring equipment:

Metre ruler = 1 mm

Signal generator ~ 10 nHz

Top-pan balance = 0.005 g

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4
Q

Method

A

This method is an example of the procedure for varying the length of the string with the frequency – this is just one possible relationship that can be tested

Set up the apparatus by attaching one end of the string to the vibration generator and pass the other end over the bench pulley and attach the mass hanger

Adjust the position of the bridge so that the length L is measured from the vibration generator to the bridge using a metre ruler

Turn on the signal generator to set the string oscillating

Increase the frequency of the vibration generator until the first harmonic is observed and read the frequency that this occurs at

Repeat the procedure with different lengths

Repeat the frequency readings at least two more times and take the average of these measurements

Measure the tension in the string using T = mg

Where m is the amount of mass attached to the string and g is the gravitational field strength on Earth (9.81 N kg–1)

Measure the mass per unit length of the string μ = mass of string ÷ length of string

Simply take a known length of the string (1 m is ideal) and measure its mass on a balance

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5
Q

Analysing the Results

A
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6
Q

Graph

A

Plot a graph of the mean values of f against 1/L

Draw a line of best fit and calculate the gradient

Work out the wave speed, which will be 2 × gradient

Verify the wave speed of the travelling waves using the equation:

Velocity Equation v= root T / u
Where:

T = tension (N)

μ = mass per unit length (kg m−1)

Assess the uncertainties in the measurements of length and the frequency and carry out calculations to determine the uncertainty in the wave speed

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7
Q

Systematic errors

A

An oscilloscope can be used to verify the signal generator’s readings

The signal generator should be left for about 20 minutes to stabilise

The measurements would have a greater resolution if the length used is as large as possible, or as many half-wavelengths as possible

This means measurements should span a suitable range, for example, 20 cm intervals over at least 1.0 m

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8
Q

Random errors

A

The sharpness of resonance leads to the biggest problem in deciding when the first harmonic is achieved

This can be resolved by adjusting the frequency while looking closely at a node. This is a technique to gain the largest response

Looking at the amplitude is likely to be less reliable since the wave will be moving very fast

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9
Q

Safety Considerations

A

Use a rubber string instead of a metal wire, in case it snaps under tension

If using a metal wire, wear goggles to protect the eyes in case it snaps

Stand well away from the masses in case they fall onto the floor

Place a crash mat or any soft surface under the masses to break their fall

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