The circuit contains two diodes each with a forward resistance of 50 \Omega and with infinite reverse resistance. If the battery voltage is 6V, the current through the 120 \Omega resistance is \underline\hspace2cm mA.

Electronic Devices PYQ — JEE Main 2021 · 26 Feb · Shift 1 · Q65 with Solution

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Correct answer: 20

Interpret the diode model

Each diode is idealized as:

forward resistance $= 50\,\Omega$
reverse resistance $= \infty$

So a forward-biased diode behaves like a $50\,\Omega$ resistor, while a reverse-biased diode behaves like an open circuit.

Identify conducting diode(s)

From the given circuit, only one diode is forward biased in the path containing the $120\,\Omega$ resistor, while the other diode is reverse biased and does not conduct.

Hence, the conducting loop contains:

battery: $6\,\text{V}$
diode forward resistance: $50\,\Omega$
resistor: $120\,\Omega$
another series resistance in the loop: $130\,\Omega$

Thus total resistance in the conducting path is

R_{\text{eq}} = 50 + 120 + 130 = 300\,\Omega

Find the circuit current

Using Ohm’s law,

I = \frac{V}{R_{\text{eq}}} = \frac{6}{300} = 0.02\,\text{A}

I = 20\,\text{mA}

Current through the $120\,\Omega$ resistor

Since the $120\,\Omega$ resistor lies in the same series conducting branch, the same current flows through it.

Therefore,

I_{120} = 20\,\text{mA}

Comparison with stored answer

Derived answer: $20\,\text{mA}$

Stored correct answer: $20$

They match.

More from Electronic Devices

View written solutionFree

Correct answer: 20

Interpret the diode model

Each diode is idealized as:

forward resistance $= 50\,\Omega$
reverse resistance $= \infty$

So a forward-biased diode behaves like a $50\,\Omega$ resistor, while a reverse-biased diode behaves like an open circuit.

Identify conducting diode(s)

From the given circuit, only one diode is forward biased in the path containing the $120\,\Omega$ resistor, while the other diode is reverse biased and does not conduct.

Hence, the conducting loop contains:

battery: $6\,\text{V}$
diode forward resistance: $50\,\Omega$
resistor: $120\,\Omega$
another series resistance in the loop: $130\,\Omega$

Thus total resistance in the conducting path is

R_{\text{eq}} = 50 + 120 + 130 = 300\,\Omega

Find the circuit current

Using Ohm’s law,

I = \frac{V}{R_{\text{eq}}} = \frac{6}{300} = 0.02\,\text{A}

I = 20\,\text{mA}

Current through the $120\,\Omega$ resistor

Since the $120\,\Omega$ resistor lies in the same series conducting branch, the same current flows through it.

Therefore,

I_{120} = 20\,\text{mA}

Comparison with stored answer

Derived answer: $20\,\text{mA}$

Stored correct answer: $20$

They match.

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