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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 current and time for the first 1010 minutes?

Options

  1. AA constant horizontal line at 24μA24 \mu\text{A}.
  2. BA linear decrease starting from 24μA24 \mu\text{A} and reaching zero.
  3. CAn exponentially growing curve starting from zero and approaching 24μA24 \mu\text{A}.
  4. DAn exponentially decaying curve starting from 24μA24 \mu\text{A} and approaching zero.

Correct answer

D. An exponentially decaying curve starting from 24μA24 \mu\text{A} and approaching zero.

Step-by-step solution

The given circuit is an RC charging circuit.

The time constant of the circuit is given by τ=RC\tau = RC.

Substituting the given values:

τ=(1.0×106Ω)×(100×10−6 F)=100 s\tau = (1.0 \times 10^6 \Omega) \times (100 \times 10^{-6} \text{ F}) = 100 \text{ s}

The initial current in the circuit at t=0t = 0 is:

I0=VR=241.0×106=24μAI_0 = \dfrac{V}{R} = \dfrac{24}{1.0 \times 10^6} = 24 \mu\text{A}

The current in an RC circuit during charging varies with time according to the equation:

I(t)=I0e−t/τI(t) = I_0 e^{-t/\tau}

I(t)=24e−t/100μAI(t) = 24 e^{-t/100} \mu\text{A}

This equation represents an exponentially decaying curve. At t=0t = 0, the current is 24μA24 \mu\text{A}, and as time progresses, it exponentially approaches zero.

For a duration of 1010 minutes (600 s600 \text{ s}, which is 6τ6\tau), the current will have decayed to a value very close to zero. Thus, the graph is an exponentially decaying curve starting from 24μA24 \mu\text{A} and approaching zero.
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