Lab D03: THE OSCILLOSCOPE

Prelab: Read Giancoli 20(10) and TWTW. Know how televisions and oscilloscopes work.

First, some settings:

· Make sure that the two red dials (labeled "variable") are turned completely clockwise and clicked

· Set the VOLTS/DIV dial to 1

· The DC/AC button should be depressed

· The ground (GND) button should be depressed

· The oscilloscope probe (the long wire with red and black alligator clips at the end) should be attached to INPUT at the bottom left corner of the oscilloscope (if it's not attached, push the connecting piece in and turn clockwise)

· Set the TIME/DIV dial to H IN

· The two dials at the top left (under VERTICAL) and top right should be depressed in

1) Turn on the oscilloscope. You should see a blue-green dot. Are you actually seeing the electrons? What are you seeing?

2) Connect the red and black alligator clips to each other. Then center the electron beam in the middle of the screen by using the dials at the top left and top right of the oscilloscope. Un-depress the push-button labeled "GND".

From this point on, do not use the very top left and right dials!

3) Attach the 2 ends of a single battery pack to the alligator clips of the oscilloscope probe by connecting the red (positive) end of the battery to the red alligator clip and the negative end of the battery to the black alligator clip. What happens to the electron beam? What apparently must the red alligator clip be connected to inside the oscilloscope? the black clip? Remember the sign of the electron charge!

4) Remember that you set the VOLTS/DIV dial to 1 volt/div. Notice that a "division" is one of the centimeter-sized marks on the screen. Predict what will happen when you turn the VOLTS/DIV dial to 2. Then try it. Repeat (predict and try) for 0.5 volt/div.

5) Predict what will happen when the battery holder connections are reversed (the red end of the battery holder to the black alligator clip, etc.). After predicting, try it.

6) Predict what will happen if you connect the 4-battery pack to the oscilloscope. What do you have to do to get it back on the screen? (Remember that you can't use the very top left and right dials!)

7) Replace the 4-battery pack with the 1-battery pack. Now turn the TIME/DIV dial to 0.1 sec. What happens? How long does it take the electron beam to move across the entire screen (all 10 divisions)? Time it. Why is this dial labeled 0.1 sec?

8) Experiment with the TIME/DIV dial. Describe what it does. At what setting must the TIME/DIV be set so that the electron beam produces a constant line? Why does eye/brain perceive a line rather than a moving electron at that setting?

9) Draw a diagram of the voltage difference between the horizontal deflection plates [i.e., Vleft - Vright ]as a function of time (for when TIME/DIV = 0.1 sec) below. Label axes appropriately. Get the shape of the graph correct first. Then add numbers to the axes where you can.

10) Disconnect the battery from the alligator clips. Hold one metal clip with one hand and the other with your other hand. What shape is the oscilloscope trace? You may have to use the VOLTS/DIV dial to fit the entire trace on the screen. And you should also experiment with the TIME/DIV dial. You may also want to increase the intensity of the electron beam. Find the period (in seconds) of the wave using the TIME/DIV dial setting. Draw a large labeled diagram in your lab book showing what you did.

11) What is the frequency of the wave? Where is this voltage signal coming from?

12) To summarize: what can oscilloscopes measure?