
Aim: to Verify the Lens Maker's Equation, using a
Converging Lens 
See The Focal Length of a Lens, Refractive Index,
The Lens Equation 

The lens maker's equation is useful to... guess
who... people who make lenses. 
The equation allows us to predict the focal length
of a lens knowing the radii of curvature of its
surfaces , r_{1} and r_{2}
and the refractive index of the
lens material, n. 
For a thin lens, surrounded by air, the equation is 

At first sight thus might seem to give a surprising
result for any symmetrical lens (having the same
curvature on both faces), namely, f = infinity. 
However, the equation is derived using a sign
convention which can be summarized as follows. 
Imagine a beam of light passing through the lens; if
it meets a convex surface, r has a positive
value and if the light meets a concave surface, r is
negative. 
From this we see that for a symmetrical lens, the
equation can be written 

Method 
It is assumed that you can get hold of some sort of
optical bench, something like that shown below. 
Also, since you will need to measure the radius of
curvature of the lens surfaces, it is convenient to use
a lens which is symmetrical (both surfaces the same
curvature). 
Measure the image distances, v
corresponding to as wide a range of object distances,
u as possible. 


Plot a graph of 1/v against 1/u
and use it to find the focal length of the lens. 

The next diagram should give you an idea of how to
find the radius of curvature of the lens surfaces. 

