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Concepts Of Physics MCQ Edition [Volume 2]
Exam
Concepts Of Physics MCQ Edition [Volume 2]
Subject
Physics
Chapter
Electric Current in Conductors

Concepts Of Physics MCQ Edition [Volume 2] · Physics · Electric Current in Conductors

A 100 capacitor is joined to a 24 V battery via a 1.0 M resistor....

A 100μF100 \mu\text{F} capacitor is joined to a 24 V24 \text{ V} battery via a 1.0 MΩ1.0 \text{ M}\Omega resistor. Which of the following best describes the qualitative graph between charge and time for the first 1010 minutes?

Options

  1. AA constant horizontal line at 2400μC2400 \mu\text{C}.
  2. BAn exponentially decaying curve starting from 2400μC2400 \mu\text{C} and approaching zero.
  3. CA linear increase starting from zero and reaching 2400μC2400 \mu\text{C}.
  4. DAn exponentially growing curve starting from zero and approaching 2400μC2400 \mu\text{C}.

Correct answer

D. An exponentially growing curve starting from zero and approaching 2400μC2400 \mu\text{C}.

Step-by-step solution

The time constant of the RCRC circuit is given by τ=RC=(1.0×106Ω)(100×10−6 F)=100 s\tau = RC = (1.0 \times 10^6 \Omega)(100 \times 10^{-6} \text{ F}) = 100 \text{ s}.

The maximum steady-state charge on the capacitor is Q0=CV=(100μF)(24 V)=2400μCQ_0 = CV = (100 \mu\text{F})(24 \text{ V}) = 2400 \mu\text{C}.

The equation for the charge on a charging capacitor as a function of time is q(t)=Q0(1−e−t/τ)q(t) = Q_0 (1 - e^{-t/\tau}).

This equation represents an exponentially growing curve that starts from zero at t=0t = 0 and asymptotically approaches the maximum charge Q0=2400μCQ_0 = 2400 \mu\text{C}.

Since the given time interval is 10 minutes=600 s=6τ10 \text{ minutes} = 600 \text{ s} = 6\tau, the capacitor will be nearly fully charged by the end of this period. Thus, the graph is an exponentially growing curve starting from zero and approaching 2400μC2400 \mu\text{C}.
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