BMSIT&M Department of Physics Engineering Physics Lab manual August-2020
Page 6
moment of inertia values of the bodies about the respective axes are determined using
the formulae indicated in the tabular column.
The circular disc is suspended using the check nuts of the experimental wire such that
the axis of suspension is perpendicular to the plane of the disc. A convenient
reference mark is made on the edge of disc, using a piece of chalk and a reference
pointer is placed just in front of the circular disc. The base of the chuck nut is twisted
through a small angle (small amplitude) such that torsional oscillations are setup. A
stop clock is started when the reference mark on the body crosses the reference stick
in a particular direction. The time taken for the reference mark on the plate to cross
the reference pointer in the same direction is taken as time for one oscillation. The
time taken for 5, 10 and 15 such oscillations is noted using a stop clock. The period
of oscillations is calculated by dividing the time taken for 10 oscillations by 10 and
the mean period of oscillation is calculated.
Again, suspend the circular disc in such a way that, the axis of the suspension passes
through the diameter of the disc. The mean period of oscillation is calculated by
repeating the above procedure.
Then circular disc is removed from the wire and the rectangular plate is suspended,
first about an axis perpendicular to the plane of the plate, next about an axis
perpendicular to the length and lastly about an axis perpendicular to its breadth.
The mean period of oscillation is calculated in each case separately. For each axis of
suspension of circular & rectangular bodies, the ratio of moment of inertia to the
square of period of oscillation i.e. (I/T
2
)
is calculated and hence, the mean value of
(I/T
2
) is calculated.
PART I: To determine moment of inertia of irregular body
The given irregular body is suspended by the experimental wire, with an axis
of suspension perpendicular to its plane or its length or its breadth of the
irregular body. The body is set in to torsional oscillation and the period of
oscillation (T
0
) is calculated.
The moment of inertia of the irregular body (I
0
) about an axis is calculated by
taking the mean value of (I/T
2
) from the regular bodies using the formula.
kgm
2
PART II: To determine the rigidity modulus of the material of the experimental wire.
The length (l) of the wire between the two chuck nuts is found by using a
thread or scale. Using the radius of the wire which is given and by noting the
mean value of (I/T
2
) of regular bodies, the rigidity modulus of the material of
the wire is calculated using the formula
mean
T
I
r
l
24
8
N/m
2
OBSERVATIONS
Mass of the circular plate M
1
= --------- Kg
Radius of the circular plate R = --------- x10
-2
m
Mass of rectangular plate M
2
= --------- Kg