Single Cantilever
Aim
To determine Young’s modulus of the given material using single cantilever.
Apparatus required
Material beam, meter scale, vernier calliper, screw gauge, slotted weights, and trav-
elling microscope.
Diagram
                                      Figure 1:
Formula used
                                              4M gL3
                        Young’s modulus q =     3
                                                      N m−2
                                              bd δavg
where M – Mass required to produce an elevation δ.
L – Distance from the fixed support to free end.
b – Breadth of the scale.
d – Thickness of the scale.
δ – Elevation produced for the load M .
Department of Physics, MUSE, Mysuru                                  Expt. 1 : 1 of 3
                                                                      Single Cantilever
Theory
Young’s modulus is defined as the ratio of the longitudinal stress to the longitudinal
starin within the elastic limits. A material whose Young’s modulus is high is consid-
ered as rigid. Hooke’s law (stress is directly proportional to strain) holds good in the
elastic range. It is a measure of stiffness of the elastic material.
                                            Longitudinal stress
                       Young’s modulus =
                                            Longitudinal strain
Tabular column
Least count of the travelling microscope:
                                    Value of 1 MSD
                          LC =                       cm.
                                 Total Number of VSD
Load Increasing (LI) Readings
  Load (M ) in gm       MSR in cm        CVD       T R = M SR + (CV D × LC) in cm
Load decreasing (LD) Readings
  Load (M ) in gm       MSR in cm        CVD       T R = M SR + (CV D × LC) in cm
To find δmean
  Load (M ) in gm       LI     LD      Average
Department of Physics, MUSE, Mysuru                                     Expt. 1 : 2 of 3
                                                                    Single Cantilever
  Load (M ) in gm      R1       Load (M ) in gm     R2      δ = R1 ∼ R2
                                                         δavg = —–cm
Calculations
Distance between the two knife edges L = 60 cm
Mass for which elevation is found M = 100 g
Breadth of the bar b = 2.5 cm
Thickness of the bar d = 2.78 mm.
Procedure
   1 The material of the given bar whose Young’s modulus is to be determined is
     fixed to a rigid suuport at a distance of L = 60 cm.
   2 The bar is loaded with 50 g at one end using weight hangers.
   3 A pin is fixed at the midpoint of the beam. It is focussed through a microscope
     and the reading is noted.
   4 Increase the load on the scale pan in steps of 50 g, till a maximum load of 200 g
     and the corresponding TM reading are noted in each case.
   5 The procedure is repeated by decreasing the load in steps of 50 g.
   6 Calculate the mean elevation for 100 g.
   7 Calculate the Young’s modulus using the given formula.
Result
The Young’s modulus of the material of the given bar =——— N m−2 .
Department of Physics, MUSE, Mysuru                                   Expt. 1 : 3 of 3