Topic 3 : PN Junction Diode Circuit

1. In the given circuits (a), (b) and (c), the potential drop across the two p-n junctions are equal in⇒  (NEET 2022 Phase 1)

NEET 2022 Phase 1 Physics - Semiconductor Electronics Question 11 English

A. Circuit (a) only

B. Circuit (b) only

C. Circuit (c) only

D. Both circuits (a) and (c)

The Correct Answer is (D)

Potential drops across the p-n junctions will be same if either both junctions are forward biased or both junction are reverse biased. In figure (a) and (c), both junctions are forward biased therefore both have same potential. In figure (b) first junction is forward biased and second junction is reverse biased, so both junctions have different potential difference.

2. Which one of the following represents forward bias diode ? ⇒  (NEET 2017)

A. NEET 2017 Physics - Semiconductor Electronics Question 104 English Option 1

B. NEET 2017 Physics - Semiconductor Electronics Question 104 English Option 2

C. NEET 2017 Physics - Semiconductor Electronics Question 104 English Option 3

D. NEET 2017 Physics - Semiconductor Electronics Question 104 English Option 4

The Correct Answer is (D)

A diode is said to be forward biased if p-side is at higher potential than n-side of p-n junction.

3. The given circuit has two ideal diodes connected as shown in the figure. The current flowing through the resistance R1 will be ⇒  (NEET 2016 Phase 2)

NEET 2016 Phase 2 Physics - Semiconductor Electronics Question 101 English

A. 2.5 A

B. 10.0 A

C. 1.43 A

D. 3.13 A

The Correct Answer is (A)

Current will not flow through D1 as it is reversed biased.

Current will flow through resistor R1, diode D2 and resistor R3

Now current i = 10/(2 + 2) = 2.5 A

4. Consider the junction diode as ideal. The value of current flowing through AB is ⇒  (NEET 2016 Phase 1)

NEET 2016 Phase 1 Physics - Semiconductor Electronics Question 97 English

A. 10 − 1 A

B. 10 − 3 A

C. 0 A

D. 10 − 2 A

The Correct Answer is (D)

Here, the p-n junction diode is forward biased, hence it offers zero resistance.

So IAB = 4 − ( − 6 ) 1 × 10 3 = 10-2 A

5. In the given figure, a diode D is connected to an external resistance R = 100 Ω and an e.m.f. of 3.5 V. If the barrier potential developed across the diode is 0.5 V, the current in the citcuit will be ⇒  (AIPMT 2015)

AIPMT 2015 Physics - Semiconductor Electronics Question 95 English

A. 20 mA

B. 35 mA

C. 30 mA

D. 40 mA

The Correct Answer is (C)

Potential difference across resistance R

= 3.5 – 0.5 = 3.0 V

Current in circuit, I = V/R = 3/100 = 30 mA

6. If in a p-n junction, a square input signal of 10 V is applied, as shown, ⇒  (AIPMT 2015 Cancelled Paper)

AIPMT 2015 Cancelled Paper Physics - Semiconductor Electronics Question 93 English

then the output across RL will be

A.

AIPMT 2015 Cancelled Paper Physics - Semiconductor Electronics Question 93 English Option 1

B.

AIPMT 2015 Cancelled Paper Physics - Semiconductor Electronics Question 93 English Option 2

C.

AIPMT 2015 Cancelled Paper Physics - Semiconductor Electronics Question 93 English Option 3

D.

AIPMT 2015 Cancelled Paper Physics - Semiconductor Electronics Question 93 English Option 4

The Correct Answer is (B)

Here P-N junction diode rectifies half of the ac wave i.e., acts as half wave rectifier.
During + ve half cycle Diode is forward biased output across RL will be

AIPMT 2015 Cancelled Paper Physics - Semiconductor Electronics Question 93 English Explanation

During –ve half cycle Diode is reverse biased output will not obtained.

7. Two ideal diodes are connected to a battery as shown in the circuit. The current supplied by the battery is ⇒  (AIPMT 2012 Prelims)

AIPMT 2012 Prelims Physics - Semiconductor Electronics Question 84 English

A. 0.75 A

B. Zero

C. 0.25 A

D. 0.5 A

The Correct Answer is (D)

Here D1 is in forward bias and D2 is in reverse bias so, D1 will conduct and D2 will not conduct.
So, the current supplied by the battery is

I = 5 10 = 0.5 A

8. In the following figure, the diodes which are forward biased, are ⇒  (AIPMT 2011 Mains)

AIPMT 2011 Mains Physics - Semiconductor Electronics Question 71 English

AIPMT 2011 Mains Physics - Semiconductor Electronics Question 71 English

A. (A), (B) and (D)

B. (C) only

C. (C) and (A)

D. (B) and (D)

The Correct Answer is (C)

p-n junction is said to be forward biased when p side is at high potential than n side. It is for circuit (A) and (C).

9. Which one of the following represents forward bias diode ? ⇒  (AIPMT 2007)

A. AIPMT 2007 Physics - Semiconductor Electronics Question 103 English Option 1

B. AIPMT 2007 Physics - Semiconductor Electronics Question 103 English Option 2

C. AIPMT 2007 Physics - Semiconductor Electronics Question 103 English Option 3

D. AIPMT 2007 Physics - Semiconductor Electronics Question 103 English Option 4

The Correct Answer is (C)

A diode is said to be forward biased if p-side is at higher potential than n-side of p-n junction.

10. Which one of the following represents forward bias diode ? ⇒  ( AIPMT 2006)

A.

AIPMT 2006 Physics - Semiconductor Electronics Question 26 English Option 1

B.

AIPMT 2006 Physics - Semiconductor Electronics Question 26 English Option 2

C.

AIPMT 2006 Physics - Semiconductor Electronics Question 26 English Option 3

D.

AIPMT 2006 Physics - Semiconductor Electronics Question 26 English Option 4

The Correct Answer is (D)

A diode is said to be forward biased if p-side is at higher potential than n-side of p-n junction.

11. Of the diodes shown in the following diagrams, which one is reverse biased ? ⇒  (AIPMT 2005)

A.

AIPMT 2004 Physics - Semiconductor Electronics Question 42 English Option 1

B.

AIPMT 2004 Physics - Semiconductor Electronics Question 42 English Option 2

C.

AIPMT 2004 Physics - Semiconductor Electronics Question 42 English Option 3

D.

AIPMT 2004 Physics - Semiconductor Electronics Question 42 English Option 4

The Correct Answer is Option (C)

A diode is said to be reverse biased if p-type semiconductor of p-n junction is at low potential with respect to n-type semiconductor of p-n junction. It is so for circuit (c).

12. In a p-n junction ⇒  (AIPMT 2002)

A. high potential at n side and low potential at p side

B. high potential at P side and low potential at n side

C. p and n both are at same potential

D. undetermined.

The Correct Answer is Option (A)

For conduction, p-n junction must be forward biased. For this p-side should be connected to higher potential and n-side to lower potential.

13. For the given circuit of p-n junction diode which is correct ⇒  ( AIPMT 2002)

AIPMT 2002 Physics - Semiconductor Electronics Question 32 English

A. in forward bias the voltage across R is V

B. in reverse bias the voltage across R is V

C. in forward bias the voltage across R is 2V

D. in reverse bias the voltage across R is 2V.

The Correct Answer is Option (A)

In forward biasing, the resistance of p-n junction diode is very low to the flow of current. So practically all the voltage will be dropped across the resistance R, i.e. voltage across R will be V.

In reverse biasing, the resistance of p-n junction diode is very high. So the voltage drop across R is zero.

14. The current in the circuit will be ⇒  ( AIPMT 2001)

AIPMT 2001 Physics - Semiconductor Electronics Question 31 English

A. 5/40 A

B. 5/50 A

C. 5/10 A

D. 5/20 A

The Correct Answer is Option (B)

D1 is reverse biased and D2 is forward biased.

∴ I = 5 30 + 20 = 5 50 A

15. From the following diode circuit, which diode is in forward biased condition ⇒  (AIPMT 2000)

A.

AIPMT 2000 Physics - Semiconductor Electronics Question 28 English Option 1

B.

AIPMT 2000 Physics - Semiconductor Electronics Question 28 English Option 2

C.

AIPMT 2000 Physics - Semiconductor Electronics Question 28 English Option 3

D.

AIPMT 2000 Physics - Semiconductor Electronics Question 28 English Option 4

The Correct Answer is Option (A)

A diode is said to be forward biased if p-type semiconductor of p-n junction is at positive potential with respect to n-type semiconductor of p-n junction. It is so for circuit (a).