[问答题]
(a) A voltmeter and an ammeter can be con
-yo )ks h41w uz dblvag-(nw92nected as shown in (F
;ezq4de5y k3 uf4q/* cdbmx *cig. Below a) to measure a resistance R. If V is the voltmeter reading, and I is the ammeter
bxq4yqud5dk43 e f;*ec /c*mzreading, the value of R will not quite be $V/I$ (as in Ohm’s law) because some of the current actually goes through the voltmeter. Show that the actual value of R is given by
$\frac{1}{R}=\frac{I}{V}-\frac{1}{R_\mathrm{V}}$,
where $R_V$ is the voltmeter resistance. Note that $R\approx V/I\quad\mathrm{if}\quad R_\mathrm{V}\gg R$ .
(b) A voltmeter and an ammeter can also be connected as shown in (Fig. Below b) to measure a resistance R. Show in this case that
$R=\frac{V}{I}-R_\mathrm{A},$
where V and I are the voltmeter and ammeter readings and $R_A$ is the resistance of the ammeter. Note that $R_\mathrm{A}\quad\mathrm{if}\quad R\approx V/I\quad\mathrm{if}\quad
R_\mathrm{A}\ll R.$
