University of the West of England

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**
Propagation of
Uncertainty** (Calculation
of resistivity)

Link to Video Answer

The electrical resistivity, *ρ* (Ω m), of a material can be found from the
following equation:

by measuring the
resistance *R *(Ω) of a wire of cross sectional area *A* (m^{2})
and length *L* (m).

The resistance, area and length of a piece of wire are measured with the values given in the table

Variable |
Value |
Standard deviation uncertainty |

Resistance, |
1.50 Ω |
0.02 Ω |

Cross
sectional area of wire, |
7.9×10 |
0.2×10 |

Length of
wire. |
0.300 m |
0.002 m |

Use Excel to calculate the

i) value
of the resistivity, *ρ*,

ii)
standard deviation uncertainty in *ρ*, and

iii) 95%
confidence interval in *ρ*.