Electronic Devices | Physics JEE previous year questions with Solutions

Q 21 :

Which of the following statement is not correct in the case of light emitting diodes? [2023]

A. It is a heavily doped p–n junction.
B. It emits light only when it is forward biased.
C. It emits light only when it is reverse biased.
D. The energy of the light emitted is equal to or slightly less than the energy gap of the semiconductor used.

Choose the correct answer from the options given below:

C and D
A
C
B

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(3)

LED works in forward biasing and light energy maybe slightly less or equal to band gap.

Q 22 :

Choose the correct statement about Zener diode [2023]

It works as a voltage regulator in reverse bias and behaves like simple p–n junction diode in forward bias.
It works as a voltage regulator in both forward and reverse bias.
It works a voltage regulator only in forward bias.
It works as a voltage regulator in forward bias and behaves like simple p–n junction diode in reverse bias.

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(1)

Works as voltage regulator in reverse bias and as simple P-N junction in forward bias.

Q 23 :

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R [2023]

Assertion A: Diffusion current in a p–n junction is greater than the drift current in magnitude if the junction is forward biased.

Reason R: Diffusion current in a p–n junction is from the n-side to the p-side if the junction is forward biased.

In the light of the above statements, choose the most appropriate answer from the options given below:

Both A and R are correct and R is the correct explanation of A
Both A and R are correct but R is NOT the correct explanation of A
A is correct but R is not correct
A is not correct but R is correct

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(3)

In forward biased condition, diffusion of majority charge carriers takes place from $p$ -side to $n$ -side which constitute the diffusion current.

Q 24 :

A zener diode of power rating 1.6 W is to be used as voltage regulator. If the zener diode has a breakdown of 8 V and it has to regulate voltage fluctuating between 3 V and 10 V. The value of resistance $R_{s}$ for safe operation of diode will be [2023]

$13.3 Ω$
$12 Ω$
$10 Ω$
$13 Ω$

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(3)

$V_{b} = 8 volt$

$V_{A} - V_{B} = 8 volt$

$Current through zener diode,$

$i = \frac{P}{V} = \frac{1.6 W}{8 V} = 0.2 A$

$V_{C} - V_{A} = 10 - 8 volt$

$R = \frac{V_{C} - V_{A}}{i} = \frac{2 V}{0.2 A} = 10 Ω$

[Note: A zener diode can regulate only if input voltage $\geq$ zener breakdown voltage. The range of input voltage should be 8 to 10V so that output voltage remains constant = 8V]

Q 25 :

If each diode has a forward bias resistance of $25 Ω$ in the below circuit,

Which of the following options is correct [2023]

$\frac{I_{3}}{I_{4}} = 1$
$\frac{I_{2}}{I_{3}} = 1$
$\frac{I_{1}}{I_{2}} = 1$
$\frac{I_{1}}{I_{2}} = 2$

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(4)

$R_{e q} = \frac{150 \times 150}{300} + 25 = 100 Ω$

$I_{1} = \frac{5}{10} = 0.05 A$

$I_{2} = I_{4} = \frac{0.05}{2} = 0.025 A$

$\frac{I_{1}}{I_{2}} = 2$

Q 26 :

The following diagram shows a Zener diode as a voltage regulator. The Zener diode is rated at $V_{Z} = 5 V$ and the desired current in the load is $5 mA$ . The unregulated voltage source can supply up to $25 V$ . Considering the Zener diode can withstand four times of the load current, the value of resistor $R_{s}$ (shown in circuit) should be ____ $Ω$ . [2026]

1000
100
4000
10

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(1)

Q 27 :

The charge stored by the capacitor C in the given circuit in the steady state is____________ $μ c .$ . [2026]

5
10
7.5
12.5

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(2)

Q 28 :

Assuming in forward bias condition there is a voltage drop of 0.7 V across a silicon diode, the current through diode $D_{1}$ in the circuit is ______ mA.

(Assume all diodes in the given circuit are identical) [2026]

18.8
17.6
20.15
11.7

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(1)

Topic Question Set

Q 22 :

Choose the correct statement about Zener diode [2023]

Q 24 :

A zener diode of power rating 1.6 W is to be used as voltage regulator. If the zener diode has a breakdown of 8 V and it has to regulate voltage fluctuating between 3 V and 10 V. The value of resistance $R_{s}$ for safe operation of diode will be [2023]

Q 25 :

If each diode has a forward bias resistance of $25 Ω$ in the below circuit,

Which of the following options is correct [2023]

Q 27 :

The charge stored by the capacitor C in the given circuit in the steady state is____________ $μ c .$ . [2026]

Q 28 :

Assuming in forward bias condition there is a voltage drop of 0.7 V across a silicon diode, the current through diode $D_{1}$ in the circuit is ______ mA.

(Assume all diodes in the given circuit are identical) [2026]

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