Physics Current Electricity BUMHS 2024
PMDC Verified Question 24 of 112
A battery has an emf of 6.0V and an internal resistance of 0.4 \(\Omega\). It is connected to a 2.60 resistor through a switch. When switch is open, the potential difference across the switch is:
A
0V
B
6.0 V
C
2.6 V
D
5.2 V
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: 6.0 V
Concept:

An open switch effectively creates a circuit with infinite resistance, halting all current flow.

Solution:

  • When the switch is Open, Current \( I = 0 \text{ A} \).


  • Because there is no current, there is zero voltage drop across the internal resistance of the battery (\(Ir = 0 \times 0.4 = 0\text{V}\)) and zero voltage drop across the external 2.6\(\Omega\) resistor (\(IR = 0 \times 2.6 = 0\text{V}\)).


  • Therefore, the entirety of the battery's EMF is "waiting" across the break in the circuit (the open switch).


  • The potential difference across the switch is exactly the full EMF: 6.0 V.


Why other options are incorrect:

  • Opt A: A closed (on) switch has 0V across it, an open switch blocks the full voltage.


  • Opt D: This would be the terminal voltage if the switch was closed (\( I = 6/(2.6+0.4) = 2\text{A} \), \( V = 2 \times 2.6 = 5.2\text{V} \)).

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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