Focusing Power

• Nonetheless, a sense of what the inverse meter is used for in science can be built up by considering different examples of its use. One of the places it is most often seen is in the study of lenses. Powerful lenses have a short focal length, meaning that they bring images seen through them into focus close to the lens, without having to stand far away from the lens to see them. The shorter the focal length of the lens, the more powerful the lens is. Lens power is measured in inverse meters (called "diopters" by opticians) to reflect this. Just divide the number one by the focal length of the lens to derive its power in inverse meters. The greater that focal length is, the lower the number of diopters, or inverse meters, it gives.
  
  

Magnification

• Curved mirrors and lenses magnify images seen through or reflected in them so that the size of the image is larger than the apparent size of the actual object. Magnification is a measurement of how much the image size is changed, and is determined by the size of the object the lens or mirror shows and the size of the image it produces. More specifically, it is the product of the height of the image in meters multiplied by the inverse of the height, in inverse meters, of the apparent size of the object itself. Using "inverse meters" here is just a way of saying that you divide the height of the image in meters by the height of the object in mirrors.
  
  

Wire Resistance

• Inverse meters are also found in measurements of the resistivity of wires. All materials, even good conductors like copper wire, resist the flow of electricity to some extent. This resistance is proportional to the length of the wire: the longer the wire, the more resistance it has. The result of this is that wire is often described in terms of its resistance per meter, meaning that the "inverse meter" is used to specify how resistant to current wire is.
  
  

Spectroscopy

• The study of light, called "spectroscopy," also uses the inverse meter as a unit. Here it is referred to as the "wavenumber," which describes waves in terms of how much space a single wavelength takes up. The wavenumber is simply the number one divided by the wavelength. It is a way of saying that the wave has "one cycle per x number of meters."
  
  

In Summary

• The inverse meter is not a physical unit. It does not directly correspond to any physical quantity like length or time. However, various sciences use it as a way of expressing things more simply than they could if they stuck only to physical units. The "inverse meter" is simply a way of saying that some physical quantity gets larger over smaller distances.