Exercise 9C: Reasoning About Circuits
The questions in this exercise can all be solved using some combination of the following ap-
proaches:
a) There is constant voltage throughout any conductor.
b) Ohm’s law can be applied to anypartof a circuit.
c) Apply the loop rule.
d) Apply the junction rule.
In each case, discuss the question, decide what you think is the right answer, and then try the
experiment.- A wire is added in parallel with one bulb.
Which reasoning is correct?- Each bulb still has 1.2 V across it, so both bulbs are still lit up.
- All parts of a wire are at the same voltage, and there is now a wire connection from one
side of the right-hand bulb to the other. The right-hand bulb has no voltage difference
across it, so it goes out.
- The series circuit is changed as shown.
Which reasoning is correct?- Each bulb now has its sides connected to the two terminals of the battery, so each now has
2.4 V across it instead of 1.2 V. They get brighter. - Just as in the original circuit, the current goes through one bulb, then the other. It’s just
that now the current goes in a figure-8 pattern. The bulbs glow the same as before.
574 Chapter 9 Circuits