Question 6
In activity 19.2, case 1 joins the positive terminals of both cells to the two terminals of the bulb. What happens?
The right answer is the one marked above.
There is no potential difference, so no current flows. Both ends of the bulb are connected to positive terminals, so they are at the same potential. With no potential difference between them nothing is pushed through the bulb.
Case 2 does the same thing with two negative terminals and fails for the same reason. Only case 3, with one of each, produces a potential difference.