Experiment 7: Focal Length and Magnification of a Thin Lens Required Equipment f

Question

Experiment 7: Focal Length and Magnification of a Thin Lens Required Equipment from Basic Optics System Light Source Bench Converging lens of unknown focal lengthI Screen Other Equipment Metrie ruler Optics Caliper (optional, for measuring image sizes), PASCO part OS-8468 Purpose The purpose of this experiment is to determine the focal length of a thin lens and to measure the magnification for a certai cobiif object anld image distances. Theory For a thin lens leg 1) where is focal length, do is the distance between the object and the lens and di is the distance between the image and the lens. By measuring doand di the focal length can be determined. Magnification, M is the ratio of image size to object size. If the image is inverted, M is negative. Part In this part, you will determine the focal length of the lens by making a single mea- surement of di with do Procedure 1. Hold the lens in one hand and the screen in the other hand. Focus the image of a distant bright object (such as a window or lamp across the room) on the screen. Have your partner measure the distance from the lens to the screen. This is the image distance, di 2. Analysis 1. As do approaches infinity,what does lido

Explanation / Answer

1) Image formes by the lens is inverted

This can be found by using the data

Since the magnification m is di/do hence in the data we can see m will come out to be negative as we put do negative and di positive

so image will be inverted

2)Image is real

this can be known because the image distance is posive means according to sign convention when di is posive means the image is other side of the lens so the rays are really passing and meeting to form image.

3)For screen to object distance there are two lens positions to get the image : This happening is called as conjugate foci

when object is between F and 2F the image is beyond 2 F and when object is beyond 2 F then the image is between F and 2 F

This can be achieved only by moving the lens and keeping object to screen distance fixed (which must be largethan the atleast four times the focal length of the lens)

4)By looking at the image we can tell the magnification is negative if the image is not towards the same side of the lens rather image is another side of the lens, not towards the same side whether object is placed. As well as if image is obtained on the screen means it is real, and real image is inverted hence the magnification is negative.

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