Refer to the circuit diagram given in the figure. Which of the following observations are correct?
A. Total resistance of circuit is $6\ \Omega$
B. Current in ammeter is $1\ \text{A}$
C. Potential across $AB$ is $4\ \text{V}$
D. Potential across $CD$ is $4\ \text{V}$
E. Total resistance of the circuit is $8\ \Omega$
Choose the correct answer from the options given below:
Answer: (A) A, B and D only
The positive terminal of the cell is at the top, so current flows through the ammeter to $C$, down to $D$, and the diode from $D$ to $A$ is forward biased (treat it as ideal, zero resistance).
From $D$ the current divides between the lower $4\ \Omega$ ($D$ to $B$) and the $4\ \Omega$ from $A$ to $B$. These are in parallel: $2\ \Omega$.
Total resistance $= 4 + 2 = 6\ \Omega$ (A correct, E wrong).
Current $I = \dfrac{6}{6} = 1\ \text{A}$ (B correct).
$V_{CD} = 1\times4 = 4\ \text{V}$ (D correct).
Each parallel branch carries $0.5\ \text{A}$, so $V_{AB} = 0.5\times4 = 2\ \text{V}$ (C wrong).
Correct: A, B and D only.
Solution by Sreeraj P, M.Sc Physics