During the charging of a capacitor through a resistor from a DC source, how does the current flowing into the capacitor change with time?

Difficulty: Easy

Correct Answer: decrease

Explanation:


Introduction:
The transient behavior of current in an RC circuit reveals how quickly a capacitor charges and how the system settles. This question probes your understanding of the current waveform during the charging phase.


Given Data / Assumptions:

  • Series RC charging from a constant DC source.
  • Capacitor initially uncharged.
  • Ideal first-order model.


Concept / Approach:
In RC charging, i(t) = (Vs / R) * exp(-t / τ). The current is maximal at t = 0 and decays exponentially to zero as the capacitor approaches the supply voltage and the net voltage across the resistor falls.


Step-by-Step Solution:
1) At t = 0, capacitor voltage is 0, so i(0) = Vs / R (maximum).2) As Vc rises, the voltage across R drops, reducing current.3) Exponential decay continues until steady state, where current ideally becomes zero.


Verification / Alternative check:
Differentiate Vc(t) = Vs * (1 - exp(-t / τ)) to see i(t) = C * dVc/dt = (Vs / R) * exp(-t / τ), confirming exponential decrease.


Why Other Options Are Wrong:
Increase: opposite of actual behavior; current is highest at the start.Remain the same: contradicts exponential law.Cannot tell: the first-order model clearly predicts the trend.


Common Pitfalls:
Assuming constant current as with an ideal current source; here the source is a constant voltage and the resistor limits current dynamically.


Final Answer:
decrease

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