Final answer:
To determine the potential difference across a used D-cell battery, use a multimeter set to measure voltage. You would expect to find a lower voltage than the 1.5 volts typical of a new D-cell, as the battery's stored chemical potential has been converted into light and heat, depleting its energy.
Step-by-step explanation:
Investigating the Potential Difference of a D-cell Battery
To determine the potential difference across a D-cell battery that kept a flashlight on all night, you need to use a multimeter set to measure voltage. Connect the multimeter's probes to the positive and negative terminals of the battery. As the battery has been used for an extended duration, it's expected to find that the measured potential difference has decreased from its initial value due to the conversion of chemical potential energy into electrical energy and subsequently into light and heat over time. A new battery typically has a potential difference of about 1.5 volts in the case of D-cells. Therefore, if the flashlight has gone out, the potential difference you measure could be well below that, possibly near or below the operational voltage required for the flashlight.
Batteries store chemical potential energy, and as they are used, this energy is converted to electrical energy which then powers a device, in this case, a flashlight. When the battery is nearly depleted, it fails to maintain the necessary potential difference across the terminals, resulting in the flashlight going out. Used batteries typically have significantly lower potential differences compared to new batteries after being turned on for the same length of time.