Work Step by Step
(a) If R1 decreases, the voltage drop across R1 and thus R2 will also decrease, leading to the rise in voltage across R3. (b) When R1 decreases, the resultant resistance of R1 and R2 also decreases, thus voltage drop falls across R2 as well as R1. (c) When switch S is closed, R3 gets short-circuited, leading the increase in the voltage drop across R1. Since voltage across R1 increases, and V = IR, current I across R1 also increases.