Imagine that a lot of water is going to flow away, and they come to a checkpoint (imagine resistance). Resistance, something that hinders the flow of current. ), the checkpoint blocked their progress, so they couldn't pass together, only a little, and the traffic volume decreased.

When the resistors are connected in series: there is only one path, and there is no choice. Oh, what a broken barrier, blocking us again and again. If it is blocked twice (or many times), the overall flow of water will first decrease and then decrease, and the flow will become less. The same is true of current.

When the resistors are connected in parallel, there are more paths and choices. "Hum, you're blocking me and I'm going the other way." Water can pass through two checkpoints at the same time, so the overall water flow becomes larger. The current is the same.

Since the change of current is known, it can be judged according to R=U/I: when U is constant, the smaller I is, the greater R is, and the total resistance in series will become larger, so the series will become larger; When I is larger, R will be smaller, and the total resistance will be smaller after parallel connection, so it will be smaller and smaller.