Example
A torch lamp takes a current of 0.3 A from a 3 V battery. Calculate its resistance.
Answer
V = 3 V
I = 0.3 A
R = \(\frac{\text{V}}{\text{I}}\)
R = \(\frac{\text{3 V}}{\text{0.3 A}}\)
R = 10 \(\Omega\)
The resistance of the lamp is 10 \(\Omega\)
Question
Calculate the reading on the ammeter in the circuit shown below.
V = 12.0 V
R = 2.7 x 103 \(\Omega\)
I = \(\frac{\text{V}}{\text{R}}\)
I = \(\frac{\text{12.0 V}}{\text{2.7 x 10}^3\Omega}\)
I = 0.0044 A = 4.4 x 10-3 A = 4.4 mA
The reading on the ammeter is 4.4 mA.
Question
3 A flows through a 240 V lamp. What is the resistance of the lamp?
R = \(\frac{\text{V}}{\text{I}}\)
V = 240 V
I = 3 A
I = \(\frac{\text{240 V}}{\text{3 A}}\)
R = 80 \(\Omega\)
The resistance of the lamp is 80\(\Omega\)