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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

The electromotive force E and the internal resistance r of a...

The electromotive force E\mathcal{E} and the internal resistance rr of a battery are 4.3 V4.3 \text{ V} and 1.0 Ω1.0 \text{ }\Omega respectively. The external resistance RR is 50 Ω50 \text{ }\Omega. The resistances of the ammeter and voltmeter are 2.0 Ω2.0 \text{ }\Omega and 200 Ω200 \text{ }\Omega respectively. The switch is thrown to the other side such that the voltmeter is now connected across the series combination of RR and the ammeter. What will be the readings of the two meters now?
The electromotive force E and the internal resistance r of a battery are 4.3 V and 1.0 respectively. The external

Options

  1. A0.1 A0.1 \text{ A}, 4.0 V4.0 \text{ V}
  2. B0.1 A0.1 \text{ A}, 4.2 V4.2 \text{ V}
  3. C0.08 A0.08 \text{ A}, 4.2 V4.2 \text{ V}
  4. D0.08 A0.08 \text{ A}, 4.3 V4.3 \text{ V}

Correct answer

C. 0.08 A0.08 \text{ A}, 4.2 V4.2 \text{ V}

Step-by-step solution

When the switch is thrown to the other side, the voltmeter is connected in parallel with the series combination of the resistor RR and the ammeter.

Resistance of the series combination of RR and the ammeter:
Rs=R+RA=50+2.0=52 ΩR_s = R + R_A = 50 + 2.0 = 52 \text{ }\Omega

Equivalent resistance of the parallel combination of the voltmeter and RsR_s:
Rp=RsRVRs+RV=52×20052+200=10400252=260063 ΩR_p = \dfrac{R_s R_V}{R_s + R_V} = \dfrac{52 \times 200}{52 + 200} = \dfrac{10400}{252} = \dfrac{2600}{63} \text{ }\Omega

Total equivalent resistance of the circuit including the internal resistance of the battery:
Req=Rp+r=260063+1.0=266363 ΩR_{eq} = R_p + r = \dfrac{2600}{63} + 1.0 = \dfrac{2663}{63} \text{ }\Omega

Total current drawn from the battery:
I=EReq=4.3266363=270.92663 AI = \dfrac{\mathcal{E}}{R_{eq}} = \dfrac{4.3}{\dfrac{2663}{63}} = \dfrac{270.9}{2663} \text{ A}

The voltmeter reading is the potential difference across the parallel combination:
V=I×Rp=270.92663×260063=4.3×26002663=111802663≈4.2 VV = I \times R_p = \dfrac{270.9}{2663} \times \dfrac{2600}{63} = \dfrac{4.3 \times 2600}{2663} = \dfrac{11180}{2663} \approx 4.2 \text{ V}

The ammeter reading is the current flowing through the series combination of RR and the ammeter:
IA=VRs=11180266352=2152663≈0.08 AI_A = \dfrac{V}{R_s} = \dfrac{\dfrac{11180}{2663}}{52} = \dfrac{215}{2663} \approx 0.08 \text{ A}

Answer: 0.08 A0.08 \text{ A}, 4.2 V4.2 \text{ V}
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