Topic: Electronic Measurements and Instrumentation
Which of the following voltmeters will have the least loading effect on a $100~k\Omega$ source?
- A. $10~k\Omega/V$, 10 V range
- B. $20~k\Omega/V$, 10 V range
- C. $1~M\Omega$ digital voltmeter
- D. $50~k\Omega/V$, 5 V range
Answer: C. $1~M\Omega$ digital voltmeter
Explanation: Loading effect in voltage measurement is minimized when the input resistance of the voltmeter is as high as possible.
Calculate the total internal resistance for each option:
(a) $10~k\Omega/V \times 10 V = 100~k\Omega$
(b) $20~k\Omega/V \times 10 V = 200~k\Omega$
(c) $1~M\Omega = 1000~k\Omega$
(d) $50~k\Omega/V \times 5 V = 250~k\Omega$
The $1~M\Omega$ digital voltmeter possesses the highest internal resistance, hence it draws the least current and introduces the least loading effect.