physics h/w help - temp. heat. expansion?

Question

1. An old remedy for a pair of nested drinking glasses that stick together is to run water at different temperatures into the inner glass and over the surface of the outer glass. Which water should be hot, and which cold?

2. Why is it important that glass mirrors used in astronomical observatories be composed of glass with a low "coefficient of expansion"?

3. Consider a pair of brass balls of the same diameter, one hollow and the other solid. Both are heated with equal increases in temperature. Compare the diameters of the heated balls.

4. Suppose that you cut a small gap in a metal ring. If you were to heat the ring, would the gap become wider or narrower? ( Wouldn't it become wider because it's expanding outward?)

Thankss..

Answer 1

1. inside cold; so it shrinks
outside hot, so it expands

2. the shape of the inside of the mirror is polished to micron accuracy. If the bottom of the mirror is warmer than the top (reflective surface), the mirror's shape will warp (due to thermal expansion) and distort the image (of the star, planet, etc.). A low coefficient of thermal expansion will help reduce distortion.

3. The solid one will be bigger, because it contains more heat (more metal = more heat, for the same temperature for each ball). More heat = more expansion.

4. The gap should close. This is the basis for a number of temperature measuring devices,

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Answer 2

The equation is substitute in ability = mass*particular warmth*temp substitute you have the substitute in ability, mass, and particular warmth, sparkling up for the temperature substitute and upload it to the 20 C temperature that the water is already at.