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

b. 5.6 mA

Step-by-step explanation:

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

`(1)/(R) = (1)/(r_1) + (1)/(r_2) = (1)/(10000) + (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.