Questions for Coefficient of Thermal Linear Expansion Lab Experiment: 1-Why must

Question

Questions for Coefficient of Thermal Linear Expansion Lab Experiment:

1-Why must the change in length, ?L be measured so carefully, while the length of the rod, L, can be measured relatively crudely with a meter stick?

2-Consider a compound bar consisting of aluminum and iron strips fastened together. What happens when it is heated?

3-When ordinary mercury thermometer is placed in hot water, its reading drops at first, but then quickly rises. Explain why.

4-A flat piece of metal has a hole in it. If the temperature increases, will the size of the hole increase, decrease, or stay the same? Explain.

5-The Golden Gate Bridge is 1280 meters in length, and is made of steel. Compute the expansion of the bridge as the temperature changes -20

Explanation / Answer

1) The initial length is a fairly large value. The error involved using a meter stick is small compared to the overall length.

In other words, say a meter stick can read accurately to 1/16 of an inch. If the total length (Li) is 20 inches, 1/16 of an inch is only .3% of the total. You are not off very far by using the meter stick with a 1/16" error.

The change in length (delta L) is small, perhaps 1/8" or so. If you try to measure that with a yardstick and introduce 1/16" error, you are now off by 50%. The error will mess up your results.

2)The expansion rate of Aluminium is about twice that of Iron.
The heated bi-metal strip will therefore bend to the side on which the Iron is fixed.

3) The ordinary mercury thermometer is made of two materials on the outside, i.e., 1- matellic bulb & 2- graded glass tube. When it is put in boiling water (temperature = 100 Celcius) the matellic bulb which is at room temeprature (20 ~ 25 Celcius) expands a little due to the coefficient of linear expansion of the matel of which the bulb is made of. So the mercury goes down in the glass tube. After fractions of moment, the matellic bulb temperature becomes equal to the boiling water and then the mercury inside the tube is heated and raises in the glass tube

4) as the temperature increases the hole increases in size. Since all distances between given material particles (atoms) expand linearly with increase of temperature, so do atoms located right on the circumference of the hole. And since the distance between them increases, so does the hole.

You apply this concept when you heat the metal lid on a jar by holding it over a flame on the stove in order to remove it more easily.

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