16. If you make a triangular pinhole using the tips of your thumb and first two

Question

16. If you make a triangular pinhole using the tips of your thumb and first two fingers you can make a ?microscope? that places a sharp ?mage of an object on your retina even ?f the object and your eye are just a few millimeters away from the pinhole. (The photo shows a similar arrangement obtained by curling a finger, but the fingertip method is far more impressive.) How can this trick work when most people cannot bring objects closer than about 25 cm into focus with the unaided eye, and your pinhole ca n not have any refractive power?

Explanation / Answer

diameter of hole=2(focal length*wavelength of light)1/2

that is

d=2(f*l)1/2

d=2(25*10-9)1/2

d=2*5*10-9/2

d=10*10-9/2

d=10-7/2 cm

by choosing diameter of hole to be 10-7/2 cm , we can get focal length 25 cm

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