Page 150 - Physics - XI

ACTIVITY - 6

Aim

To study the eff ect of load on depression of a suitably clamped metre scale loaded at (i) its end (ii) in the
middle.

Apparatus and Materials Required

A uniform wooden metre scale, two G-clamps, pointer pin, wax or adhesive tape, thread, slotted
weights of 50 g each, vertical scale, and clamp stand

Principle/Theory

The depression δ of a cantilever of length l loaded at its free end with a weight mg is given by
mgl 3
δ =
4 Ybd 3
where, b = width of the rectangular cantilever
d = thickness of the rectangular cantilever
Y = Modulus of elasticity of the material.

For a given l, Y, b and d from the above equation we have
δ ∝ mg
i.e. depression is proportional to the load (weight) suspended from the other end.

Procedure
(i) When metre Scale is loaded at its end
1. Clamp a uniform and strong wooden meter scale fi rmly with G-clamp at the edge of a table such that
the metre scale is in a horizontal plane and a suitable length (say 60–70 cm) of its projects beyond the

edge of the table.
2. Fix a pointer (a metallic pin with fi ne tip) with the free end of the metre scale with the help of either
wax or adhesive tape. Check that pointer remains horizontal.
3. Take a clamp stand and fi x a measuring scale as shown in Fig. 6.1 in it such that scale is perfectly

vertical. Pointer
4. Note the initial reading on vertical scale
corresponding to the tip of the pointer when no load
is suspended from the metre rod. 50 40 30 20 10

5. Suspend a suitable weight (say 50 g) from the zero Metre rod
mark of the metre rod with the help of a thread so
that a small depression takes place there. Note the G-clamp Slotted weights
reading on vertical scale corresponding to the tip of
the pointer. Scale

6. Gradually increase the weight in the step of 50 g
and every time note reading on the vertical scale. Fig. 6.1: Experiment set up to study the eff ect

of load on depression of a metre scale

148