In an experiment to measure the resistivity of nichrome, the resistance, the diameter and appropriate length of a sample of nichrome wire were measured - Leaving Cert Physics - Question 4 - 2009

1. Zeroing the Instrument: Use a micrometer or digital calipers to measure the diameter. Ensure the device is zeroed before measuring.

2. Place the Wire: Insert the wire between the jaws of the micrometer or calipers ; ensure it's secured appropriately without compressing it.

3. Tighten the Jaws: Gently tighten the jaws to just touch the wire without applying excessive force.

4. Take the Reading: Read the measurement displayed on the micrometer or caliper.

5. Repeat the Measurement: Move the wire slightly and take additional readings at different points along the wire to ensure accurate results.

6. Calculate the Average Diameter: Add all the readings together and divide by the number of measurements to find the average diameter.

To calculate the resistivity ($\rho$) of nichrome, use the formula:

$\rho = \frac{R \cdot A}{L}$

where:

• $R$ = resistance of wire = 7.9 Ω
• $A$ = cross-sectional area = $\pi r^2$, where $r = \frac{d}{2}$ and $d = 0.31 \text{ mm} = 0.31 \times 10^{-3} \text{ m}$
• $L$ = length of wire = 54.6 cm = 0.546 m.

1. Calculate Area: $r = \frac{0.31 \times 10^{-3}}{2} = 0.155 \times 10^{-3} \text{ m}$ $A = \pi (0.155 \times 10^{-3})^2 = 7.55 \times 10^{-8} \text{ m}^2$

2. Substitute Values: $\rho = \frac{(7.9)(7.55 \times 10^{-8})}{0.546} \approx 1.092 \times 10^{-6} \Omega \text{ m}$

On a warmer day, the resistance of the nichrome wire would likely increase due to the increase in temperature, which causes the atoms in the wire to vibrate more and impede the flow of electrons. This could lead to an increase in the measured resistance, as per the relationship between temperature and resistivity.