Page 819 - Basic Electrical Engineering

readings are taken of the quantity and through statistical analysis the best
approximation about the true value is arrived at.

Example 11.2 Calculate the error due to the loading effect of a voltmeter

used to measure voltage across the terminals in the circuit as shown in Fig.
11.9. The voltmeter is having an internal resistance of 925 kΩ.

Figure 11.9 Loading effect illustrated

Solution:

Voltage across terminals A and B,

Note that voltage across the 50 kΩ resistor is the same as voltage across
terminals A and B. That is voltage across terminals MN is the same as across

terminals AB.
Thevenin’s equivalent resistance across terminals A and B is calculated by
replacing the EMF source by its internal resistance which is zero in the case.

Hence, we just short the voltage source and calculate the equivalent
resistance across terminals AB as shown in Fig. 11.10.

Figure 11.10