Resistors???

Question

Resistors R1 and R2 are connected in series to a battery. A) What happens to the current through R1 when a third resistor R3 is connected parallel with R2?

B) What happens to the current through R1 when a third resistor R3 is connected in series with R2?

thanks...

Answer 1

Suppose battery =V

Initially without R3,

   current in R1 = V/(R1 + R2)

After R3 om parallel to R2.

Effective resistance = R1 + (R2*R3 / (R2 + R3))

Current in R1 = V/[R1 + (R2*R3 / (R2 + R3))]

Connecting resistance in parallel decreases overall resistance and thus current increases.

If instead R3 is in series,

  Eff Res = R1 + R2 + R3

Current in R1 = V/[R1 + R2 + R3]

Connecting resistance in series increases overall resistance and thus current decreases. Try putting sample values of say 1 ohm each for R1, R2 and R3

Answer 2

a) Connecting R3 in parallel with R2 lowers the effective resistance through the circuit, so by V = IR (and voltage is not changed), the current through R1 will increase.

b) Connecting R3 in series with R2 raises the effective resistance through the circuit, so the current will decrease.