Explain why adding more identical resistors in series to a circuit causes the current in the circuit to decrease, whilst adding more identical resistors in parallel to a circuit causes the current drawn from the supply to increase.

In a series circuit the resistors are connected end‑to‑end, so the total resistance is the sum of the individual resistances. Adding more identical resistors therefore increases the total resistance. According to Ohm’s law, I = V/R, a larger R gives a smaller I for the same supply voltage, so the current in the circuit decreases.

In a parallel circuit each resistor is connected across the same two points, giving an extra path for current. Adding more identical resistors therefore creates more parallel branches. The equivalent resistance of parallel resistors decreases as more branches are added, so the total resistance of the circuit is lower. With a lower R the current drawn from the supply increases (I = V/R).