AP Physics C 2017

(E)

4 . The circuit shown in the figure has a battery with an emf of 24 V and an internal resistance of 1 Ω.
When operating as shown, what is the terminal voltage (VXY ) of the battery?
(A) 24 V
(B) 18 V
(C) 16 V
(D) 8 V
(E) 6 V

Answers

1 . D —Adding the 1 Ω and 2 Ω resistor in series produces an equivalent resistance of 3 Ω. Next, add
the resulting 3 Ω resistor to the 2 Ω resistor in parallel to produce the required 1.2 Ω resistor:

Note    that    both    choices A   and D   will    produce an  equivalent  resistance  of  1.  2   Ω.  However,    choice  D

only    needs   two 2   Ω   resistors,  whereas choice  A   needs   five    2   Ω   resistors,  making  choice  D   a   more

effective   and cheaper solution.

2 . C —With the switch open, the circuit is a simple series circuit with an equivalent resistance of 2R.
Both ammeters will receive the same current: