A student sketches the voltage across a capacitor as it charges in an circuit
PHYSICS · Single correct · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
A student sketches the voltage across a capacitor as it charges in an RC circuit. The sketch begins at 12V at t=0 and decreases asymptotically toward 0V as time increases. Which feature of the student’s sketch reveals a conceptual error about the charging process?
(a) The curve is asymptotic rather than linear, suggesting the voltage should rise at a constant rate.
(b) The curve approaches 0V instead of rising toward the 12V battery voltage.
(c) The curve has its steepest slope right after t=0, which would not occur if the capacitor were charging properly.
(d) The curve never actually attains its final value in a finite time; a correctly drawn charging curve would reach the battery voltage after one time constant.