Basic Idea:

• Examine the optical properties of lenses.

	What:	How Many:	Where:
	Optical bench (see setup diagram)	1	Majors storeroom, shelf P5 & P6
	Optical bench riders (see picture below)	4	Majors storeroom, shelf P4
	Lens/screen holder (see picture below)	2	Majors storeroom, shelf P3
	Arrow object (see picture below)	1	Majors storeroom, shelf N4
	Screen    (translucent plastic with an index card) (see picture below)	1	Majors storeroom, shelf N4
	Light bulb & holder (bulbs are painted black)	1	Majors storeroom, shelf N4
	Virtual image detector (meter stick with attached lenses – see below)	1	Majors storeroom, shelf Q4
	800–series converging lens (mount this on optical bench)	1	non-Majors storeroom, shelf KK3
	Extra converging lenses   marked with series	Several boxes (leave on instructor's bench)	non-Majors storeroom, shelf KK3
	Diverging (negative) lenses	One box (leave on instructor's bench)	non-Majors storeroom, shelf KK3
	Small, mounted converging lenses (marked with an A)	1	non-Majors storeroom, shelf KK3
	Blue Variac	1	non-Majors storeroom, shelf L3
	Meterstick	1	non-Majors storeroom, shelf AA1
	Meterstick calipers	2	non-Majors storeroom, shelf AA3

Computers Needed?

• No.

• Lab setup (See this page for photo details. Make sure that the bulb and arrow object face the window, as shown below. Also note how the optical benchs are placed; make sure that the ruler on the optical bench always faces the outer edge of the lab bench, again as shown):

  

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• Optical bench components:
  • Note #1: The screen is a translucent piece of plastic with a blank index card taped to it. Make sure the index card side faces the lens.
  • Note #2: Do not use the optical bench riders that are screwed closed; use only the ones that can be tilted sideways (easier to move them out of the way without removing from the optical bench).

  

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• Optical bench setup detail:

  

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• Virtual image detector (see usage instructions below):

  

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  Adjusting the virtual image detector:

• The following adjustments should be made before the start of lab:
  1. Move the screen and pointer so they are separated by 60 cm (20 cm from each end).
  2. Adjust the lens so that a sharp image of the pointer appears on the screen.

  

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  Using the virtual image detector:

• When the object distance is less than the focal length of the lens, the virtual image detector must be used:
  • Students should observe that no image is produced on the optical bench screen, no matter it's location.
  • Stand at the end of the optical bench, look through the lens at the arrow object. Students will see the upright, magnified, virtual image.
  • Show students that the image of the pointer is produced by the small lens of the image detector on the small screen (check the adjustment before lab begins).
  • Hold virtual image detector as shown in picture below. Move the detector back and forth until an image of the arrow object appears on the small screen. The location of the first image, therefore, must be at the pointer of the image detector.
  • Students then measure the virtual image distance. Note: this measurement is less accurate than others!

  

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• Part I needs to be completed with the windows uncovered; they should be covered for part II.

• The lenses are marked with a series number, related to the diopter strength. So, for 800 series lenses: ¹/₈₀₀ = 0.00125, so the focal length would be f = 12.5 cm! Note that the markings are inconsistant (sometime the inverse of the marking is multiplied by 1000).

• Only use 800 or 900 series lenses, not 400! The optical benches are not long enough.