Physics Current Electricity ETEA 2018
PMDC Verified Question 94 of 112
A cell of internal resistance 2.0\(\Omega\) and electromotive force (e.m.f) 1.5V is connected to a resistor of resistance 3.0\(\Omega\) what is the potential difference across 3\(\Omega\) resistor.
A
5V
B
1.2V
C
0.9 V
D
0.6V
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: 0.9 V
Concept:

The potential difference across the external resistor is the same as the terminal voltage of the cell.

Formula:

$$ I = \frac{E}{R+r} \quad \text{and} \quad V = IR $$

Solution:

  • First, calculate total current: \( I = \frac{1.5 \text{ V}}{3.0 \, \Omega + 2.0 \, \Omega} = \frac{1.5}{5} = 0.3 \text{ A} \).


  • Now, find voltage across the external resistor \( R \): \( V = I \times R \).


  • \( V = 0.3 \text{ A} \times 3.0 \, \Omega = 0.9 \text{ V} \).


Why other options are incorrect:

  • Opt B: Might occur from incorrect resistance ratios.


  • Opt D: 0.6V is the voltage drop inside the cell (\( Ir = 0.3 \times 2.0 = 0.6\text{V} \)), not across the external resistor.

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