discuss experimental determination of Young's modulus of a metallic wire
Answers
Explanation:
AIM :-
✴️ To determine Young’s modulus of elasticity of the material of a given wire.
Apparatus :-
✴️Searle’s apparatus, two long steel wires of same length and diameter, a metre scale, a screw gauge, eight 1/2 kg slotted weights and a 1 kg hanger.
Description of Searle’s Apparatus:-
▪️Construction:- Searle’s apparatus consists of two metal frames F1 and F2. Each frame has torsion head at the upper side and hook at the lower side. These frames are suspended from two wires AB and CD of same material, length and cross-section. The upper ends of the wires are screwed tightly in two torsion heads fixed in same rigid support.
▪️A constant weight of 1 kilogram is suspended from the hook of the frame F2 attached to the auxiliary wire CD, which keeps the wire taut. A hanger H of 1 kilogram weight is suspended from the hook of the other frame F1. The experimental wire AB can be loaded by slipping slotted weights on the hanger.
▪️A spirit level rests horizontally with its one end hinged in the frame F2. The other end of the spirit level rests on the tip of a spherometer screw fitted in the frame F1. The spherometer screw can be rotated up and down along a vertical pitch scale marked in millimetre. The two frames are kept together by cross bars E1 and E2.
Working.:-
▪️To perform the experiment, kinks are removed from the wire AB by loading and unloading it two or three times. All the weights are then removed from the hanger. The wire AB is kept taut under the weight of the hanger alone.
▪️The spherometer screw is then rotated till the bubble comes in the middle of the spirit level. The spherometer disc reading is recorded for zero load.
▪️A half kilogram weight is now slipped in the hanger. The wire AB extends and the frame F: moves down. The levelling is disturbed. The distance by which screw is turned upwards gives the elongation of the wire due to half kilogram weight. A number of observations are taken by increasing the load on the hanger in steps of half kilogram each. The observations are then repeated by decreasing the load in the same order till all the weights are removed from the hanger.
▪️A graph is plotted between load M and mean extension l. It is a straight line. From the graph, mean increase in length l for a load M kg is found.