MEASUREMENT OF RADIUS OF CURVATURE OF A LENS WITH A SPHEROMETER EXPERIMENT

 

Title of experiment: Measurement of radius of curvature of a lens with a spherometer

APPARATUS: Spherometer, piece of plate glass, the Plano convex lens

METHOD: I observed the scale given on top of the horizontal vernier scale. This enabled me to make the necessary unit conversion point of touch, with the vernier scale. This was added to the last reading to be taken on the vernier scale as the measurement proceeded.

THEORY

From the figure above AC * CB = DC * CE

i.e. L^2 = h(2R – h)

    h = distance through the centre leg is screwed up when it touches the lens surface

   R = radius of curvature of lens

Then L^2 = 2RH – h^2

       Or k = L^2 + h^2 / 2h

Thus R can be calculated.

MEASUREMENT:

       Place the spherometer on the glass slap and screw the centre leg to adjust touch the glass surface. See that the zeros of both scales coincide otherwise make for the zero error. Screw up the center leg, the place the lens with the relevant surface. Place the spherometer on it and screw down the centre leg to touch the surface of the lens. Ensure that all the other three legs press the spherometer on a piece of paper with the centre leg screwed down and the distance (L) between the center and outer leg obtained.