If R1 = 30 ohms, R2 = 15 ohms, R3 = 10 ohms, and the current through R2 is 4 amps, what is the source voltage?

To determine the source voltage in this circuit, we start by considering the arrangement of the resistors and the fact that the current through R2 is given as 4 amps.

Using Ohm's Law, V = I × R, we can find the voltage across R2 first. Since R2 has a resistance of 15 ohms and the current through it is 4 amps, the voltage across R2 can be calculated as follows:

Voltage across R2 = Current through R2 × Resistance of R2

= 4 A × 15 ohms

= 60 volts.

This voltage represents the potential difference across R2, which would also be the total voltage supplied by the source if R1 and R3 are in series with R2 or if R2 is connected directly with the source. In many common configurations, particularly in series circuits or when discussing active voltage drops, the voltage across a resistor corresponds to the source voltage.

Thus, the source voltage of 60 volts is consistent with the current flowing through R2 and its resistance, which justifies why the correct answer is 60 volts.