Experiment 2.13  
THE CONVERGING LENS

PROCEDURE


1.    Open up the Lens Workbook, and fill in the header information.

2.    Set up the equipment as shown in Fig. 2.13-1. Turn on the light source and slide the lens toward or away from the crossed arrow target to focus the image of the target onto the viewing screen. Answer Questions 1 through 3 on the Worksheet.
 
 

 

Fig 2.13-1: The Converging Lens Set Up

3.    Remove the light source and the crossed arrow target and then move the viewing screen backward or forward to get a sharp image of an object that is distant, or "far away". An object that is more than 7.5 meters (about 25 feet) should be sufficiently "far away" as shown in Fig. 2.13-2. The object distance is so large that we may consider it to be infinitely large. This means that the quantity (1/do) is zero and di = f. In this manner, we can directly measure the focal length. Record this length (in mm) in cell E33.

4.    Reposition the light source and the crossed arrow target on the bench.
 

In the following procedure, you will set do to the values (in millimeters) listed below.

do (mm) = 500, 450, 400 , 350 , 300 , 250 , 200 , 150 , 100

Record the height of the object in cell E39, and use Edit...Fill...Down to place the same value in all the cells in the column E40:E47.

At each object distance setting you should perform the following measurements:
 

  • Move the viewing screen to get a sharp image and measure and record di in cells D39:D47.
  • Measure and record hi, the height of the image in cells F39:F47.
     
When finished, the table in cells C39:F47 should be completed.
5.    Next, try do = 70 mm and then 50 mm. At each of these do values you will not be able to find an image that will focus on the screen.  Try looking back through the lens at the object and determine what the nature of the image is. Discuss your observations in Questions 4 and 5 on the Worksheet.