Work Step by Step
When the switch is closed, the effective resistance of the parallel resistors becomes smaller. This combination is in series with R1 and the battery, and the circuit’s entire resistance gets smaller. A greater current flows through the battery, and through R1. This results in a larger voltage drop across R1. The voltage from the battery equals the sum of the voltages across R1 and across R4. Therefore, increasing the voltage across R1 reduces the voltage across R4.