Practical 4 - Determination of Young Modulus of a metal in the form of a wire Flashcards
How do we plot the graph in this practical?
Applied load along the y-axis
Extension along the x-axis
What goes along the y-axis?
Applied load (F)
What goes along the x-axis?
Extension
Which formula can we use for calculating the Young modulus using a graph?
E = gradient x l
—
A
How do we calculate the area of the wire?
πr^2
What do we need two of in this practical?
2 wires - 1 test wire and 1 comparison wire
What should be similar between the test wire and the comparison wire in this practical and why?
They should be made of the same material so that temperature changes will have the same affect on both
Describe the features of the test wire and explain why
-should be as thin as possible
-should be as long as possible
(To obtain a measurable extension)
How do we obtain a measurable extension in this practical?
-using a wire as thin and as long as possible
What does using a wire as thin and as long as possible give us in this practical?
A measurable extension
What is set up to measure the extension of the test wire?
A vernier arrangement
What does the vernier arrangement do in this practical?
Measure the extension of the test wire
What are the wires hanging off of?
A support beam
What’s attached to the comparison wire and why?
A small fixed weight to keep the wire straight
How do we keep the comparison wire straight?
Attach a small fixed weight
What’s attached to the test wire?
A variable load
How do we measure the diameter of the wire?
Using a micrometer
What does a micrometer do in this practical?
Measures the diameter of the wire
Why do we measure the diameter of the wire at various different points?
To calculate a reliable mean diameter
What’s the method for this practical?
- Hang 2 identical wires from a beam
- Attach a scale to the first wire and a small weigh to keep it straight
- Put a small weight on the second wire to straighten it and a Vernier scale linking with the scale on the comparison wire
- Measure the original length of the test wire and its diameter (using a micrometer) at various points along its length
- Calculate a mean cross-sectional area
- Place a load on the test wire and find the extension. Repeat up that least 50N
- Plot the graph and calculate the gradient and use this to find the value for the Young modulus
Precautions for this practical
Repeat readings
Measure the diameter pf wore in multiple different places
Keep temperature constant
Ensure no kinks in wire
Wire securely clamped
Stay within the elastic limit
Use of longer wire
Avoid parallax
