Question

During an experiment with a meter bridge, the galvanometer shows a null point when the jockey is pressed at $40.0\, cm$ using a standard resistance of $90 \Omega$, as show in the scale used in the meter bridge is $1\, mm$. The unknown resistance is

• A. $60 \pm 0.15\, \Omega$
• B. $135 \pm 0.56\, \Omega$
• C. $60 \pm 0.25\, \Omega$
• D. $135 \pm 0.23 \,\Omega$

Answer 1

Answer: (C)

$60 \pm 0.25\, \Omega$

Answer 2

$R =\frac{ x }{100- x } 90$
$\therefore R =60\, \Omega$
$\frac{ dR }{ R }=\frac{100}{( x )(100- x )} dx$
$\therefore dR =\frac{100}{(40)(60)} 0.1 \times 60$
$=0.25 \,\Omega$
Alternatively
$\frac{ dR }{ R }=\frac{0.1}{40}+\frac{0.1}{60}$
$\therefore dR =0.25 \,\Omega$