What isfocal lengthof lens

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Focal length diagramchart

Hamamatsu Photonics K.K. has been recognized by IEEE (Institute of Electrical and Electronics Engineers, corporate headquarters: New York, NY), the world’s largest professional organization for the advancement of technology in the areas of electronics, information technology and telecommunications, for technical achievement in the development of the 20-inch photomultiplier tube (PMT), which has been used for the observation of phenomena such as supernovas and neutrinos.

For a magnifying lens to work the object is placed close to the convex lens ie. between the lens and the focal point. Draw a ray diagram to show how such a lens would work. Hint: you need to label both the object and image in your diagram and to think about where the image appears to be.

Q. An object of height 8 cm is placed in front of a lens. It's inverted image of height 4.8 cm is formed on the screen. If the focal length of the lens is 12 cm then by drawing at scale calculate the object distance, image distance and magnification.

Focal lengthof lens formula

For its contribution to the observation of neutrinos, the 20-inch PMT has been certified as an IEEE Milestone, which IEEE describes as an award that recognizes “technological innovation and excellence for the benefit of humanity found in unique products, services, seminal papers and patents” in one of the technical areas represented by IEEE.

Once you have it, join this point to the optical centre (the centre of the lens) and extend this ray (in purple) to meet the original incidence ray. Where they meet is where the object is.

Focal length diagramray

If you know the height of the object, you can draw a ray that is parallel to the optical axis. And you should know how that gets refracted from the lens. Similarly, if you know the height of the (inverted!) image you can draw a ray parallel to the optical axis that will (now propagating in the opposite direction) get refracted by the lens. Now, these two rays are enough for you because at their intersections you get both the object and the image.

Taking scale as 1cm = 4cm I've drawn the principal axis and the lens and marked focus (F) at 3cm from the lens. But how do I proceed from here with only the heights of the object and image?!

Extend both rays as much as you can (line in blue). Then, from the optical axis on the image side, find the perpendicular length of image that corresponds to the image length (the base is the focal axis and the tip of the image is where the image meets the refracted ray initially drawn).

Do you know how to draw the image of an object set at a certain distance from the lens? It is sort of the inverse. Start by drawing the ray parallel to the optical axis from the object incident onto the lens and refracted through the focus $F$.

The 20-inch PMT was originally developed by Hamamatsu at the request of Masatoshi Koshiba (Professor Emeritus, University of Tokyo), who jointly won the 2002 Nobel Prize in Physics for his research on the detection of cosmic neutrinos. Initially, hundreds of the 20-inch PMTs were manufactured and installed in the Kamioka Proton Decay Experiment. Subsequently, over ten thousand 20-inch PMTs were installed in the Super-Kamioka Neutrino Detection Experiment.