Physics Photo of the Week

February 13, 2009

Magnifying Lens

If a simple lens that is thicker in the middle than on the edges is held close to an object, the image appears magnified and enlarged.  This simple magnifier is the most common use of a simple lens.  Another common use of a simple lens is to view a distant object shown in PPOW of November 30, 2007
Unlike the real inverted image when the lens is held at arm's length to examine distant objects, the image produced by the simple magnifier is a "Virtual" image.  It doesn't cast light onto a screen.  The location of the virtual image is behind the lens.  Actually it is further away than the object although the photograph doesn't prove that.

Drops of liquid also make simple lenses.  The surface tension of a drop of liquid on a glass surface causes the top of the liquid to be curved.  Since the liquid has a refractive index, the curved surface forms a simple convex lens.  The picture at right was made by placing a drop of honey on a piece of glass.  The glass was placed on a textbook-sized copy of the Periodic Table of the Elements.  The drop of honey forms a similar magnifying lens to magnify the atomic mass of Si - the most abundant element in Earth's crust.  Honey was much more effective than water to make this demonstration for two reasons: it has a high refractive index or refractive power, and it stays "beaded" up to form a convex shape on the top section as in the drawing below.

Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department.  These photos feature interesting phenomena in the world around us.  Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation.  Atmospheric phenomena are especially welcome.  Please send any photos to 

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