Edexcel A-Level Physics Substitution into Equations

Review substitution into equations in Edexcel A-Level Physics through modulus, strain and luminosity calculations using measured quantities.

[Maximum number: 3]

A strain gauge is a sensor made from metal foil fixed to a plastic sheet, as shown.

Figure for Question C.2.3—Substitution into equations question 1 — Edexcel A-Level Physics AS

Bending the plastic sheet changes the dimensions of the metal foil.
This changes the resistance of the metal foil.
A student connected the strain gauge into the circuit shown below.

The student adjusted the variable resistor in the circuit so that the reading on the voltmeter was 0.0 mV .

He attached the strain gauge to a wooden metre rule. He clamped the metre rule to hang over the edge of a bench, as shown.

The student attached a 500 g mass to the metre rule at a distance L from the centre of the strain gauge.

The strain ε can be calculated using

ε = 6WL/(Ebt²)

where W is the weight of the 500 g mass, E is the Young modulus of the wood, b is the width of the metre rule and t is the thickness of the metre rule.

Show that ε is about 1.5 × 10⁻³.
E = 11.9 GPa
L = 0.513 m
b = 25.3 mm
t = 5.8 mm

\varepsilon=\frac{6 W L}{E b t^{2}}

where
W is the weight of the 500 g mass
E is the Young modulus of the wood
b is the width of the metre rule
t is the thickness of the metre rule.
Show that $\varepsilon$ is about $1.5 \times 10^{-3}$
E=11.9 GPa
$L=0.513 \mathrm{~m}$ $b=25.3 \mathrm{~mm}$ $t=5.8 \mathrm{~mm}$

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C.2.3—Substitution into equations question 1