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Question
The resistance of the rheostat shown in the figure is 30 Ω. Neglecting the meter resistance, find the minimum and maximum currents through the ammeter as the rheostat is varied.
Sum
Solution
Current will be minimum when the rheostat will have maximum resistance, i.e 30 Ω.
In this case, total resistance of the circuit = \[\frac{20 \times 10}{30} + 30 = 36 . 67 \Omega\]
The minimum current through the circuit,
\[i_\min = \frac{5 . 5}{36 . 67} = 0 . 15 A\]
Current will be maximum when the rheostat will have minimum resistance, i.e. 0 Ω.
In this case, total resistance of the circuit = \[\frac{20 \times 10}{30} = 6 . 67 \Omega\]
The maximum current through the circuit,
\[i_\max = \frac{5 . 5}{6 . 67} = 0 . 825 A\]
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