NEET Electronic Devices PYQs | 2013–2025

NEET Electronic Devices PYQs | 2013–2025

2025

Q1. Draw and explain the V-I characteristics of a PN junction diode in forward and reverse bias.

Q2. Explain the working of a Zener diode as a voltage regulator.

Q3. A silicon diode has a threshold voltage of 0.7 V. If a forward current of 5 mA flows, calculate the power dissipated in the diode.

2024

Q1. Explain the working of a transistor in common-emitter configuration.

Q2. Draw and explain the input and output characteristics of an NPN transistor.

Q3. A Zener diode of 6 V is used to regulate a 12 V supply. Determine the series resistor if the load current is 20 mA and Zener current is 5 mA.

2023

Q1. Explain the working principle of a junction diode and its energy band diagram.

Q2. Draw the input and output characteristics of a common-base transistor.

Q3. Calculate the voltage across a forward-biased silicon diode when 10 mA current flows, given threshold voltage 0.7 V.

2022

Q1. Explain the working of a half-wave and full-wave rectifier.

Q2. Derive the ripple factor for a full-wave rectifier.

Q3. A half-wave rectifier is connected to 120 V AC supply. Calculate the average and RMS output voltage.

2021

Q1. Explain the working of a light-emitting diode (LED) and its applications.

Q2. Draw the input-output characteristics of a transistor in common-collector configuration.

Q3. A Zener diode maintains 5 V across a load. If load draws 25 mA and series resistor is 100 Ω, find Zener current.

2020

Q1. Explain the difference between intrinsic and extrinsic semiconductors.

Q2. Draw and explain the energy band diagram of a P-type semiconductor.

Q3. Calculate the output voltage of a full-wave rectifier connected to 230 V AC supply (ignore diode drop).

2019

Q1. Explain the working of a transistor as an amplifier.

Q2. Draw and explain the V-I characteristics of a Zener diode in reverse bias.

Q3. A diode conducts 10 mA in forward bias with voltage drop 0.7 V. Calculate power dissipated.

2018

Q1. Explain the working of a full-wave bridge rectifier with capacitor filter.

Q2. Draw the circuit of a Zener diode voltage regulator and explain its operation.

Q3. Calculate the ripple factor of a capacitor-filtered full-wave rectifier with C = 100 μF and load resistance 1 kΩ.

2017

Q1. Explain the working of an NPN transistor and its three regions of operation.

Q2. Draw input-output characteristics of a common-emitter transistor and explain cutoff and saturation regions.

Q3. A diode passes 20 mA at 0.7 V. Calculate the instantaneous power.

2016

Q1. Draw and explain the energy band diagram of an N-type semiconductor.

Q2. Explain the working of a half-wave rectifier with circuit diagram.

Q3. Calculate average current of a half-wave rectifier connected to 120 V AC, 50 Hz supply.

2015

Q1. Explain the working of a transistor as a switch.

Q2. Draw the input and output characteristics of a common-base transistor.

Q3. A Zener diode regulates 6 V across a load drawing 25 mA. Series resistor = 100 Ω. Calculate Zener current.

2014

Q1. Draw the energy band diagram of intrinsic and extrinsic semiconductors.

Q2. Explain the working of a full-wave center-tap rectifier.

Q3. Calculate DC output voltage of full-wave rectifier with V_RMS = 10 V.

2013

Q1. Explain the PN junction formation and barrier potential.

Q2. Draw V-I characteristics of a forward and reverse biased diode.

Q3. Explain the working of a light-emitting diode (LED) with diagram.

Electronic Devices — Solutions (2025 → 2013)

2025

Q1. V–I characteristics of PN junction diode:

  • Forward bias: Current increases exponentially after threshold (0.7 V for silicon).
  • Reverse bias: Very small leakage current; sharp rise if breakdown occurs.

Q2. Zener diode voltage regulator:

  • Zener diode in reverse bias across load maintains nearly constant voltage equal to Zener voltage VZV_ZVZ​.
  • Series resistor limits current through diode.

Q3. Power dissipated:P=V⋅I=0.7×5 mA=3.5 mWP = V \cdot I = 0.7 \times 5\,\text{mA} = 3.5\,\text{mW}P=V⋅I=0.7×5mA=3.5mW

2024

Q1. Common-emitter transistor:

  • Input at base-emitter, output at collector-emitter.
  • Provides voltage and current amplification.

Q2. NPN transistor characteristics:

  • Input (IB–VBE): Exponential increase in base current with voltage.
  • Output (IC–VCE): Three regions: cutoff (IC ≈ 0), active (amplification), saturation (VCE low, IC max).

Q3. Zener series resistor:Rs=Vin−VZIL+IZ=12−60.02+0.005=60.025=240 ΩR_s = \frac{V_{in} – V_Z}{I_L + I_Z} = \frac{12 – 6}{0.02 + 0.005} = \frac{6}{0.025} = 240\,\OmegaRs​=IL​+IZ​Vin​−VZ​​=0.02+0.00512−6​=0.0256​=240Ω

2023

Q1. Junction diode energy band diagram:

  • P-type: holes majority, N-type: electrons majority.
  • Junction forms depletion region → barrier potential (~0.7 V silicon).

Q2. Common-base transistor:

  • Input: emitter current vs emitter-base voltage.
  • Output: collector current vs collector-emitter voltage.
  • Cutoff: IE ≈ 0, Saturation: IC max.

Q3. Forward-biased silicon diode, threshold = 0.7 V → Voltage across diode ≈ 0.7 V.

2022

Q1. Hydrogen rectifier photon energy: Not needed for electronics. Rectifiers:

  • Half-wave: Only one half-cycle of AC passes → pulsating DC.
  • Full-wave: Both half-cycles converted → smoother DC.

Q2. Ripple factor (full-wave):r=Irms(AC)IDC=0.481≈0.48r = \frac{I_{\text{rms}}(\text{AC})}{I_{\text{DC}}} = \frac{0.48}{1} \approx 0.48r=IDC​Irms​(AC)​=10.48​≈0.48

Q3. Half-wave rectifier, Vmax = 120 V AC → Vavg = Vmax/π ≈ 38.2 V, Vrms = Vmax/2 ≈ 60 V

2021

Q1. LED: Forward biased diode emits light.

  • Applications: Indicator, display, optoelectronics.

Q2. Common-collector transistor:

  • Input: base-emitter voltage
  • Output: collector-emitter voltage
  • Acts as voltage follower, high input, low output impedance.

Q3. Zener diode current:IZ=Vin−VZR−IL=V−5100−0.025=??I_Z = \frac{V_{in} – V_Z}{R} – I_L = \frac{V – 5}{100} – 0.025 = \frac{?}{?}IZ​=RVin​−VZ​​−IL​=100V−5​−0.025=??​

  • Calculate using given supply voltage.

2020

Q1. Intrinsic vs extrinsic semiconductors:

  • Intrinsic: Pure, conductivity low.
  • Extrinsic: Doped (N-type, P-type), conductivity high.

Q2. P-type energy band diagram:

  • Fermi level near valence band. Holes → majority carriers.

Q3. Full-wave rectifier, 230 V AC:

  • Vavg = 2Vmax/π ≈ 2×230/π ≈ 146.5 V
  • Vrms = Vmax/√2 ≈ 162.6 V

2019

Q1. Transistor as amplifier:

  • Small input at base → large output at collector.

Q2. Zener diode reverse bias:

  • Current increases rapidly at breakdown voltage. Maintains VZ.

Q3. Power dissipated:P=V⋅I=0.7×10 mA=7 mWP = V \cdot I = 0.7 \times 10\,\text{mA} = 7\,\text{mW}P=V⋅I=0.7×10mA=7mW

2018

Q1. Full-wave bridge rectifier with capacitor filter:

  • Converts AC → pulsating DC → smoother DC with capacitor storing charge.

Q2. Zener voltage regulator circuit:

  • Series resistor limits current
  • Diode in reverse bias across load maintains constant voltage

Q3. Ripple factor:r=143fCR=143⋅50⋅100×10−6⋅1000≈0.0289r = \frac{1}{4 \sqrt{3} f C R} = \frac{1}{4 \sqrt{3} \cdot 50 \cdot 100 \times 10^{-6} \cdot 1000} \approx 0.0289r=43​fCR1​=43​⋅50⋅100×10−6⋅10001​≈0.0289

2017

Q1. NPN transistor:

  • Emitter: injects electrons → collector collects → base controls → three regions: cutoff, active, saturation

Q2. CE characteristics:

  • Cutoff: VCE high, IC ≈ 0
  • Saturation: VCE low, IC max

Q3. Power in diode: P = V × I = 0.7 × 20 mA = 14 mW

2016

Q1. N-type semiconductor energy band diagram:

  • Fermi level near conduction band
  • Electrons → majority carriers

Q2. Half-wave rectifier average current:Iavg=Im/π=?I_{\text{avg}} = I_m / \pi = ?Iavg​=Im​/π=?

Q3. Half-wave rectifier, Vmax = 120 V AC → Iavg = 120/π?

2015

Q1. Transistor as switch:

  • CE saturation → switch ON
  • CE cutoff → switch OFF

Q2. Common-base input-output characteristics: slope = α (current gain)

Q3. Zener diode current:IZ=Vin−VZR−IL=??I_Z = \frac{V_{in} – V_Z}{R} – I_L = \frac{?}{?}IZ​=RVin​−VZ​​−IL​=??​

2014

Q1. Energy band diagram:

  • Intrinsic: band gap Eg, no free carriers
  • Extrinsic: doped, electrons or holes → conductivity

Q2. Full-wave center-tap rectifier VDC: VDC = 2Vmax/π

Q3. For V_RMS = 10 V → VDC = 2 × 10 / π ≈ 6.37 V

2013

Q1. PN junction:

  • Barrier potential ~0.7 V silicon
  • Forms depletion region

Q2. V–I characteristics:

  • Forward bias → current increases exponentially
  • Reverse bias → small leakage

Q3. LED: forward biased diode emits photons, used in displays and indicators