PhysicsLAB Resource Lesson
Converging Lens Examples

Directions: As you review these problems work out each example on your own paper, boxing in your answers as you go. Make sure that you state the formulas and list each problem's givens prior to solving for any requested numerical answers. Although polished rays diagrams are not required, sketches for each situation are recommended. Since this is a demonstration lesson, you may view correct answers as often as necessary to verify that you understand the steps in each problem set. Once all four problems are completed, then you are ready to proceed to your first individual worksheet.
 
To calculate the location of the image we use the thin lens equation
 



Refer to the following information for the next four questions.

When rays from the distant sun pass through a convex lens a bright point image of the sun is cast 0.7 meters behind the lens onto the ground.
Which of the original six cases applies to this problem?





 
What is the focal length of the lens? 

Is the image real or virtual? upright or inverted? 

What is the magnification? 

Refer to the following information for the next four questions.

A light bulb is placed 300 cm from a convex lens of focal length 50 cm.
Which of the original six cases applies to this problem?





 
Calculate where the image is formed. 

Is the image real or virtual? upright or inverted? 

What is the magnification? 

Refer to the following information for the next four questions.

A light bulb is placed 300 cm from a convex lens of focal length 500 cm.
Which of the original six cases applies to this problem?





 
Calculate where the image is formed. 

Is the image real or virtual? upright or inverted? 

What is the magnification? 

Refer to the following information for the next six questions.

A slide is placed 50 mm from a projector's lens. Despite all efforts, no clear, crisp, focused image can be produced on a screen regardless of the projector's distance from the screen.
Which of the original six cases applies to this problem?





 
Calculate the focal length of this original lens. 

If the slide remains in the same location but a second lens having a focal length of 49.6 mm is substituted for the original lens, at what distance from the projector should the screen now be placed to produce a focused image? 

What is the magnification? 

Which of the original six cases applies to this problem?





 
How should the slide be placed into the projector so that the image on the screen is "correct?"
 





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