Question

A voltmeter has an internal resistance of 10 000 Ω and is used to measure the voltage across a 47.0-Ω resistor that, without the voltmeter connected, has a current of 1.20 A pass through it. How much current is drawn away from the circuit by the voltmeter when it is connected across the resistor? a. 4.7 mA b. 5.6 mA c. 1.205 A d. 0 A

Answer 1

Answer:

b. 5.6 mA

Explanation:

As the voltmeter is connected to the resistor in parallel. The new resistance of the systems is

$\frac{1}{R} = \frac{1}{r_1} + \frac{1}{r_2} = \frac{1}{10000} + \frac{1}{47} = 0.0214$

R = 1/0.0214 = 46.78 Ω

The voltage is

$U = r_2 I_1 = 47 * 1.2 = 56.4 V$

So the new current now of the system is

$I_2 = U/R = 56.4/46.78 = 1.2056 A$

So about 1.2056 - 1.2 = 0.0056 A or 5.6mA is drawn away.