To find focal length of a convex lens by plotting graphs between 'u' and 'v' or between 1/u and 1/v and 1/v. | Physics Practical Class 12 |

 To  find focal length of a convex lens by plotting graphs between 'u' and 'v' or between 1/u and 1/v and 1/v.

Aim: -

To  find focal length of a convex lens by plotting graphs between 'u' and 'v' or between 1/u and 1/v and 1/v.

APPARATUS: -

Optical bench, convex lens, uprights, needles, lens holder.

THEORY: -

OBSERVATIONS: -

Length of the knitting needle (x)                 =    .................... cm

Observed distance between L and O (y)       =    .................... cm

Observed distance between L and I (z)        =    .................... cm

Index correction for u = (x -y)                     =    .................... cm

Index correction for v = (x - z)                    =    .................... cm

Rough focal length of the convex lens        =    .................... cm

TABLE: Determination of Focal Length

Mean f = ............ cm.

CALCULATIONS: -

Do yourself

RESLUT: -

The focal length of the convex lens is : 

(i)    By graph between u and v     =     ....................... cm.

(ii)    By graph between 1/u and 1/v     =    ................. cm.

PRECAUTIONS: -

1.    The tips of the needles and the center of the lens should be at the same height.

2.    Parallax must be removed tip to tip.

3.    The index correction should be taken into account.

4.    The uprights carrying the lens and the needles should not be shaky.