# Determining the diameter of a piece of Nichrome wire by determining its resistivity

Candidate Name:

Session: May 2015                 Page |

International Baccalaureate Diploma Program (IBDP)

Session: May 2015

Physics HL Lab Report

Lab Report Title: Determining diameter using resistivity.

Criteria Assessed:

• Data Collection and Processing (DCP)
• Conclusion and Evaluation (CE)

Candidate Name:

Candidate Number:

International School, Singapore

AIM: To determining the diameter of a piece of Nichrome wire by determining its resistivity.

INTRODUCTION:

Metals have low resistance due to their delocalized field of electrons. However, different metals have different values of resistance. In this experiment, the students were given a spool of Nichrome wire to determine its diameter. Nichrome, as the name suggests, is an alloy of Nickel, Chromium and Iron.

The resistance of a conductor depends on its inherent resistivity (ρ), length (l) and its cross-sectional area (A). The resistance is given by the following formula (#1): . Where,

R = Resistance (Ω)

ρ = Resistivity (Ω.m)

l = length (m) and,

A = cross-sectional area of the conductor.

To determine the cross-sectional area of the wire, the diameter was first determined using a micrometer screw gauge. The formula (#2) that relates the diameter to the cross sectional area of the wire is:

The electrical resistance can be determined by an ohmmeterlength, using a ruler, and the resistivity was determined by the literature value of 1.25×10-6 Ω.m.

Substituting the literature value for Nichrome’s resistivity () and formula #2 into formula #1, the following equation can be obtained:  This equation can graphically represented by l on the y-axis and R on the x-axis. The gradient would then give the value for which could then be manipulated to extract the value of d.

VARIABLES:

Independent Variables:

1. Length of the wire used. (l)

Dependent Variables:

1. Resistance of the circuit. (Ω)

Controlled Variables:

1. Voltage of the circuit. (V) – The same power source was used for all trials of the experiment.
2. Texture of the Nichrome wire. – It was wiped clean of any contaminants such as oxides etc.
3. The measuring tape – The same measuring tape was used to measure all heights.

PROCEDURE:

A simple circuit was set up with the Nichrome wire as the ...