[img]2012q1/ct_etoefm_etoefspeakc_1066_20121[/img] Now listen to part of a ta

Narrator 2: Number 6. Listen to part of a talk. Then listen for a question about it. After you hear the question, you have 20 seconds to prepare and 60 seconds to record your answer.
Narrator 1: Now listen to part of a talk in a biology laboratory. The teaching assistant is explaining how to use the microscope. Teaching Assistant: All right, now that you all have microscopes at your tables, I want to explain how they work and how to use them. First of all, you should know that they are compound microscopes so they can magnify objects up to 1000 times their size. These microscopes have two systems—an illuminating system and an imaging system. You’ll see that the illuminating system has a light source built in, and you can control it by adjusting the lever on the side. Why is this important? Well, the specimen must be pretty thin, or let’s say, transparent enough to let light pass through it. So the light Source controls the amount of light that passes through the specimen. Okay. The other system provides magnification. Use this lever to switch powers. So, when you switch to a higher power, you see a larger image, and when you switch to a lower power, you see a smaller image. But, I should remind you that the field of view is smaller at a higher power. In other words, at a higher magnification, you see a larger image of a smaller area. Okay.
So what about the focus? Well, these microscopes are parfocal, and that means you usually don’t have to refocus when you switch to a higher or lower power of magnification. But there are two adjustment knobs--the larger one for coarse adjustment and the smaller one for fine adjustment just in case.
Narrator 1: Using the main points and examples from the talk, describe the two major systems of the laboratory microscope, and then explain how to use it.
Narrator 2: Please prepare your answer after the beep.
Beep
[Preparation time: 20 seconds]
Narrator 2: Please begin speaking after the beep.
Beep
[Recording time: 60 seconds]
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