(Solved): electrical circuits   (a) Phe circuit shown in Figure 1 can be used to measure the resistanc ...

electrical circuits

 

(a) Phe circuit shown in Figure 1 can be used to measure the resistance of a Platinum resistance thermometer (PRT). AB is a uniform resistance mire of length \( 1.00 \mathrm{~m} \) and \( \mathrm{C} \) is a sliding contact on this wire. A standard resistor \( R \) is included in the circuit. The position of \( C \) is adjusted until the roltmeter \( V \) reads zero. Figure 1 For use in question 4 . (i) By applying Kirchhoff's laws to loops ADCA and BCDB, deduce an expression for the resistance of the PRT in terms of \( l_{1}, l \) and the value of the standard resistor. (ii) The PRT consists of \( 9.00 \mathrm{~m} \) of wire of diameter \( 8.5 \times 10^{-2} \mathrm{~mm} \). The voltmeter reads \( 0 \mathrm{~V} \) when \( l_{1}=0.415 \mathrm{~m} \). If the standard resistor: \( \mathrm{R} \), has a resistance of \( 220 \Omega \mathrm{R} \), what is the resistivity of platinum? Show that you have checked that the value for the resistivity and its unit are sensible. b) Indicate briefly what factors might affect the precision of the measurement when using such a simple circuit to measure the resistanee of the PRT.