The circuit below consists of a variable resistor connected in series with two 2000 Ω resistors. The variable resistor can be adjusted to any value between 0 - 4000 Ω.
As the resistance of the variable resistor is changed, what is the smallest possible reading on the voltmeter?
A. 0 V
B. 3 V
C. 4 V
D. 6 V
Answer.
Voltage in a series system is divided by the resistors connected in series .
- The voltage drop across a resistor is proportional to the resistance across which it is being measured.
- Therefore, for the 2000 Ohm resistor to have the minimum possible voltage across it, the other resistors must have larger resistance values so they can have the maximum voltage across them.
- Thus the variable resistor will have a value of 4000 Ohms .
The reading on the voltmeter will hence be V=2000/(2000+2000+4000) x 12
V=3V
Therefore, the correct answer is, B .