Question

The resistance of the rheostat shown in the figure (32-E5) is 30 Ω. Neglecting the meter resistance, find the



minimum and maximum currents through the ammeter as the rheostat is varied.

Answer 1

Current will be minimum when the rheostat will have maximum resistance, i.e 30 Ω.
In this case, total resistance of the circuit = $\frac{20\times 10}{30}+30=36.67\mathrm{\Omega }$
The minimum current through the circuit,
$i_{\min }=\frac{5.5}{36.67}=0.15\mathrm{A}$
Current will be maximum when the rheostat will have minimum resistance, i.e. 0 Ω.
In this case, total resistance of the circuit = $\frac{20\times 10}{30}=6.67\mathrm{\Omega }$
The maximum current through the circuit,
$i_{\max }=\frac{5.5}{6.67}=0.825\mathrm{A}$