Two resistors of 100 Ω each are connected in series with a 9V battery. A voltmeter of 400 Ω resistance is connected to measure the voltage drop across one of the resistors. The voltmeter reading i $s____V.$
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Question

Two resistors of 100 Ω each are connected in series with a 9V battery. A voltmeter of 400 Ω resistance is connected to measure the voltage drop across one of the resistors. The voltmeter reading i $s____V.$

Options

G1 Physics · Accepted Answer

The 400 Ω voltmeter is connected in parallel with one of the 100 Ω resistors. Their parallel equivalent is R(parallel) = (100×400)/(100+400) = 80 Ω. This is in series with the other 100 Ω resistor. Therefore, R(total) = 100+80 = 180 Ω. Circuit current is I = 9/180 = 1/20 A. The voltmeter measures the voltage across the 80 Ω parallel branch: V = I×80 = (1/20)×80 = 4 V. Correct option: C.

Two resistors of 100 Ω each are connected in series with a 9V battery. A voltmeter of 400 Ω resistance is connected to measure the voltage drop across one of the resistors. The voltmeter reading i s____V.