Plusivo DMM - Example

6.6.1 Example
To measure the internal resistance of a 9 V battery, we need to measure the voltage
of the battery first.
Figure 30. The measured voltage in this figure is 8.96 V DC.
Second, we connect a resistor with the battery and measure its voltage, in our case
we will connect a 510 Ω resistor.
Figure 31. The measured voltage in this figure is 8.50 V DC.
Third, we will do some calculations using Ohm’s law.
● Calculate the current passing through the resistor:
𝑅
𝑉
𝑅
= 𝐼
8.50 𝑉
510 Ω
= 0. 0167 𝐴 = 16. 7 𝑚𝐴
● Subtract the voltage of the battery from the voltage of the resistor:
𝐵
𝑉
− 𝑅
𝑉
= 𝐵
𝑅𝑉
8. 96 𝑉 − 8. 50 𝑉 = 0. 46 𝑉
● Now, we have the current and the voltage on the internal resistance, so we can
calculate the value of the internal resistor:
𝑉
𝐼
= 𝐼
𝐵𝑅
0.46 𝑉
0.0167 𝐴
= 27. 54 Ω
40
Mastering the Art of Measurement (Digital Multimeter) r.01 www.plusivo.com