Page 817 - Basic Electrical Engineering

Figure 11.8 Loading effect illustrated

To calculate the value of R we had taken current flowing through it as 5 mA.
In fact, this has not been the case. Current through R is I .
R

I = I – R = 5 mA – 0.8 mA = 4.2 mA
V
R
The actual resistance value,

Measurement error in percentage

Now, let us examine the effect of using a voltmeter of high input impedance
in this measurement. Let the sensitivity of the voltmeter be 5000 Ω/V instead

of 1000 Ω/V.

The voltmeter resistance,
R = 5000 × 100 W
V
= 500 kΩ