<p>A circuit consists of two 130-k&#937; resistors in series with an ideal 18.0-

Question

<p>A circuit consists of two 130-k&#937; resistors in series with an ideal 18.0-V battery. <br /><br />a) Calculate the potential drop across one of the resistors.</p>
<p>9.00 V (this answer is correct)<br /><br />b) A voltmeter with internal resistance 12.5 M&#937; is connected in parallel with one of the two resistors in order to measure the potential drop across the resistor. By what percentage will the voltmeter reading deviate from the value you determined in part (a)?</p>

Explanation / Answer

(b) The addition of the voltmeter resistance is going to affect the equivalent resistance of one of the 130k resistors. To figure out the equivalent resistance, use the parallel resistor equation: Req = 1/[(1/130,000)+(1/12,500,000)] = 128.66k Now the circuit can be viewed as if you have two resistors in series, 130k and 128.66k. To figure out the voltage drop over the 128.66k resistor: V = 18V*[128.66k/(128.66k + 130k)] = 8.95V The reading is 0.05V less than the 9V you expect, so percentage = 0.05/9 = 0.56%

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