Jokes about rheostat

In figure 1, the sliding rheostat is connected in series, and AC is equivalent to short circuit aR, obviously there is no current;

Fig. 2: The sliding rheostat is connected in parallel, which can be regarded as that the first half of the rheostat is connected in parallel with R and then in series with the second half of the rheostat; But it can't be seen that the current directly passes through the sliding rheostat through the a-b path;

The equivalent circuit diagram is as follows: