• id: JME-08-N14
• title: Searle's Apparatus for Young's Modulus
• tags: experiment, searle, measurement

Searle's apparatus uses two identical wires — one reference, one experimental — suspended from the same rigid support. A known load ($F$) is applied to the experimental wire and the extension ($\Delta L$) is measured using a spirit level or micrometer. $Y$ is calculated from $Y = FL/(A\Delta L)$. The reference wire compensates for thermal expansion and support yielding. Sources of error: (1) kinks in the wire, (2) inaccurate diameter measurement (use screw gauge at multiple points), (3) exceeding elastic limit. The diameter measurement is the largest source of error since $A = \pi d^2/4$ and $Y \propto 1/d^2$.