A portable data-logger powers up by charging a capacitor through a resistor from a…
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
A portable data-logger powers up by charging a 47μF capacitor through a resistor from a regulated 5.0V source. The capacitor must attain at least 95 percent of its final potential difference in no more than 12ms so that the internal reference voltage is sufficiently stable before measurements begin.
(a) Determine the minimum number of time constants that ensure a capacitor in an RC charging circuit has reached at least 95 percent of its final potential difference.
(b) Using the requirement in part (a), calculate the largest resistor value that will meet the 12ms timing specification. Give your answer in ohms.
(c) For the resistor found in part (b), calculate the magnitude of the current through the resistor at the instant right after the circuit is energized.