JEE Main 2026 — Apr 4, Shift 1 — Physics solution

JEE Main2026Apr 4, Shift 1Physics

Consider a circuit consisting of a capacitor ( $20 μ$ F), resistor ( $100 Ω$ ) and two identical diodes as shown in figure. The resistance of diode under forward biasing condition is $10 Ω$ . The time constant of the circuit is $α \times 1 0^{- 3}$ s. The value of $α$ is ______________.

A
$2.2$
B
$2.0$
C
$2.1$
D
$2.4$

Solution

For the charging path, only the forward-biased diode conducts (the other is reverse-biased and open). The active circuit is a series RC with

$R_{eff} = R + r_{d} = 100 + 10 = 110 Ω.$

Time constant: $τ = R_{eff} \cdot C = 110 \times 20 \times 1 0^{- 6} = 2200 \times 1 0^{- 6}$ s $= 2.2 \times 1 0^{- 3}$ s.

$∴ α = 2.2.$

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