A nichrome wire of circular cross-section is to be used to make a laboratory resistor of 20Ω. The wire available has diameter 0.40mm and resistivity 1.10×10−6Ωm. Answer the following parts.
(i) Write the mathematical relation connecting the resistance of a uniform wire with its length, cross-sectional area and resistivity.
(ii) Calculate the length of wire required to obtain the desired resistance.
(iii) If the maximum current that can safely pass through the wire is 0.50A, determine the highest potential difference that may be applied across the finished resistor.