Electronics MCQs for MDCAT Practice

Physics section, Electronics chapter. Up to eight free sample questions, each with the correct answer and a worked explanation. The full chapter opens in the app.

1. Question 1
   If an AC voltage of 100V peak value is applied as input to a half wave rectifier and then a full wave rectifier, the rms values of outputs will be respectively:
   • A35V and 35V
   • B35V and 70V
   • C50V and 70V (correct answer)
   • D70V and 140V
   Correct answer: C

   Calculates RMS output voltage for half-wave and full-wave rectifiers given peak input voltage, testing understanding of rectifier efficiency.
2. Question 2
   In a p-n junction, there is no appreciable current if
   • Ap-section is made positive and n-section negative
   • Ba potential difference is applied across the junction making p-section negative and n-section positive (correct answer)
   • Ca potential difference is applied across the junction
   • Dit is impossible
   Correct answer: B

   Reverse biasing a p-n junction creates a wide depletion region, blocking significant current flow and explaining why option B is correct.
3. Question 3
   The anode of a diode is 0.2 volts positive with respect to its cathode. Is it forward biased?
   • AYes, because any positive voltage at the anode causes forward bias. (correct answer)
   • BYes, because the anode is at a higher potential than the cathode.
   • CNo, because the anode must be negative relative to the cathode for forward bias.
   • DNo, because the voltage is too low to overcome the barrier potential.
   Correct answer: A

   Forward biasing of a diode occurs when the anode is at a higher potential than the cathode, allowing current flow.
4. Question 4
   In which of the following, output is similar to NAND gate if input A=0 and input B = 1.
   • ANOR.
   • BXNOR.
   • CXOR. (correct answer)
   • DBoth B and C.
   Correct answer: C

   The XOR gate's output for inputs A=0 and B=1 matches the NAND gate's output, making XOR a correct equivalent in this specific scenario.
5. Question 5
   In n-p-n transistor, p works as
   • ACollector
   • BEmitter
   • CBase (correct answer)
   • DAny of these
   Correct answer: C

   In an NPN transistor, the 'P' region refers to the p-type semiconductor material forming the base, which controls current flow between emitter and collector.
6. Question 6
   In the breakdown region zener behaves like a
   • AConstant current
   • BConstant voltage (correct answer)
   • CConstant resistance
   • DNone of them
   Correct answer: B

   Zener diodes act as constant voltage sources in their breakdown region, making them ideal for voltage regulation applications.
7. Question 7
   Which of the following is not correct regarding Zener diodes?
   • AIt is used as a half-wave rectifier (correct answer)
   • BIt is used as a shunt regulator
   • CIt is used as an AC voltage stabilizer
   • DBoth B and C
   Correct answer: A

   Zener diodes excel at voltage regulation but are unsuitable for basic rectification tasks, which are typically handled by standard diodes.
8. Question 8
   The electrical conductivity of an intrinsic semiconductor at room temperature is low mainly because:
   • AIt has a large forbidden energy gap
   • BIt contains no charge carriers
   • CIt has a very few charge carriers (correct answer)
   • DIts atoms do not vibrate
   Correct answer: C

   Intrinsic semiconductors have low conductivity at room temperature due to a limited number of thermally generated charge carriers (electrons and holes).

Read the full Electronics chapter notes: Electronics notes. Or browse every chapter.