A resistor is connected directly to an ideal 1.5 V battery in a simple closed circuit. Point A is defined at the end of the resistor where conventional current enters, and point B is at the end where current exits. A digital voltmeter has two identical probes: red (+) and black (−).
The student uses the meter to measure various potential differences within the circuit.
(a) The red probe is placed at A and the black probe at B. Predict whether the meter will display a positive value, a negative value, or zero. Explain your reasoning, referring to the motion of positive charge and changes in electric potential.
(b) The probes are now reversed (red at B, black at A). Predict the sign of this second reading and justify your answer.
(c) Finally, the student measures the battery by placing the red probe on the battery’s positive terminal and the black probe on the negative terminal. Explain how this third reading relates to those in parts (a) and (b) and to conservation of energy for a charge making one complete trip around the loop.