Two resistors r1 and r2 are connected in series to a battery with no internal resistance. the current through each is measured. a third resistor, r3, is then connected in parallel to r2. how does this affect the currents through r1 and r2?

Current in R1 will increase

Current in R2 will decrease

Explanation:

Initially two resistors are connected in series

So the net resistance of two resistors is given as

now the current through two cells is given as

now we connect a third resistor across parallel to R2

so we have

so now the net resistance of all three will be less than the initial resistance when only two resistance were there

So the value of current through Resistance R1 will increase while this current will divide in R2 and R3 so the value of current in R2 will decrease

god i hope this !