Physics Current Electricity ETEA 2018
PMDC Verified Question 91 of 112
A typical mobile phone of 5.0 V and an internal resistance of 200 m\(\Omega\). What is the terminal P.D of the battery when it supports a current of 500 mA?
A
4.8V
B
4.9V
C
5.0 V
D
5.1V
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: 4.9V
Concept:

When a battery supplies current, the terminal potential difference drops below the EMF due to internal resistance.

Formula:

$$ V_t = E - Ir $$

Solution:

  • EMF \( E = 5.0 \text{ V} \).


  • Internal resistance \( r = 200 \text{ m}\Omega = 0.2 \, \Omega \).


  • Current \( I = 500 \text{ mA} = 0.5 \text{ A} \).


  • Voltage drop inside battery = \( Ir = 0.5 \text{ A} \times 0.2 \, \Omega = 0.1 \text{ V} \).


  • Terminal voltage \( V_t = 5.0 - 0.1 = 4.9 \text{ V} \).


Why other options are incorrect:

  • Opt A: Results from a math error or using wrong decimal places.


  • Opt C: Assumes an ideal battery with zero internal resistance.


  • Opt D: Would represent a battery being charged, not discharging.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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