PASSAGE 18

Researchers at the University of Texas at Austin have used a new form of laser technology called single molecule spectroscopy to make important contributions to understanding the motion of molecules in super-cooled liquids, a problem of interest to scientists for more than half a century. The article announces both the discovery of a successful method for observing the movement of individual molecules as well as new insights into molecular motion in a material just before it turns into a glass. When liquids freeze to become solid, the molecules arrange themselves into organized structures. Super cooled liquids, in contrast, are cooled so fast that they go below freezing before the molecules have a chance to organize. If you lower the temperature of a super cooled liquid, the molecules move slower and slower until eventually the material is so cold that all motion has stopped. Then you have a different kind of solid you have a glass, an amorphous solid. If you look at the motions of molecules in super cooled liquid, you discover that they do not look like the motions of molecules in regular liquid. The researchers focused on the rotation of molecules just before this glass transition. In a normal liquid, all the molecules rotate at the same rate, which means only one time scale is involved. The researchers wanted to find out what happens to the rotation of molecules in a super cooled liquid and whether all molecules in a super cooled form were rotating in the same way at the same time, or whether each molecule was rotating at a different rate. The researchers made refinements in previously used laser technology to isolate and illuminate a very bright orange molecule called Rhoda mine 6G. Because the method allowed molecules to be observed individually, the researchers were able to avoid the jumbling effect that masks what is really happening. What they discovered is that the rotations of individual molecules are all very different from each other. Some of the molecules are moving really fast, and some are really slow. In super-cooled liquid, there are regions within the liquid that are different from one another, researchers said.

1. The author of the passage perceives research and understanding of the motion of molecules in super-cooled liquids as
A. speculative B. controversial C. inconclusive D. confirmatory E. deductive

2. The molecules of a super-cooled liquid move slower and eventually stops, under which of the following conditions?
A. When super-cooled liquid is frozen.
B. When the temperature is increased.
C. When the temperature is lowered.
D. When molecules organize into structures.
E. When the liquid is cooled fast.

3. Which of the following can be inferred from the passage about our understanding of super-cooled liquids?
A. Laser technology was not used earlier to study the motion of molecules in super-cooled liquids.
B. Previous researchers failed to observe the jumbling effect that hid what was really happening.
C. The new single molecule spectroscopy permits isolation and observation of molecules individually.
D. In super-cooled liquids, cooling takes place after the molecules become organized structures.
E. Motion of molecules in super-cooled liquids continues at a uniform rate even at extreme low temperatures.

4. Which of the following regarding rotation of molecules can be inferred from the passage?
A. Uniform rate of rotation of molecule is not observed in normal liquids.
B. There is no differentiation in the rotation of molecules in a super-cooled liquid.
C. The rotation of molecules appeared different with different methods used for observation of molecular motion.
D. Only one time scale is required when the molecules rotate at different rules.
E. There is no uniformity in the rotation of molecules in a super-cooled liquid.

Ans.

1-c
2-c
3-c
4-e