30 MCQs on the topic "Semiconductor and Electronics" for Class 12 students, with answers and brief explanations:

 

What type of bonds are present in a semiconductor?
a) Monovalent
b) Bivalent
c) Trivalent
d) Covalent
Answer: d) Covalent
Explanation: Electrons are shared between atoms forming covalent bonds in semiconductors.

The number of electrons in the valence shell of a semiconductor atom is:
a) 1
b) 2
c) 3
d) 4
Answer: d) 4
Explanation: Semiconductors like silicon have four valence electrons forming covalent bonds.

What happens to the forbidden energy gap of a semiconductor when temperature falls?
a) Decreases
b) Increases
c) Unchanged
d) Sometimes decreases or increases
Answer: b) Increases
Explanation: The energy gap increases slightly as temperature decreases.

In a P-type semiconductor, current conduction is mainly due to:
a) Holes
b) Atoms
c) Electrons
d) Protons
Answer: a) Holes
Explanation: P-type semiconductors conduct due to positively charged holes.

What is the main function of a transistor?
a) Simplify
b) Amplify
c) Rectify
d) All of the above
Answer: b) Amplify
Explanation: Transistors are primarily used to amplify signals.

In semiconductors, conduction is caused by:
a) Electrons only
b) Holes only
c) Both electrons and holes
d) Neither electrons nor holes
Answer: c) Both electrons and holes
Explanation: Both electrons and holes act as charge carriers in semiconductors.

What happens to the resistance of a semiconductor upon heating?
a) Increases
b) Decreases
c) Remains the same
d) First increases, then decreases
Answer: b) Decreases
Explanation: Resistance decreases because more electrons gain energy to conduct.

In intrinsic semiconductors at room temperature, the number of electrons and holes are:
a) Unequal
b) Equal
c) Infinite
d) Zero
Answer: b) Equal
Explanation: In pure semiconductors, electrons and holes exist in equal numbers.

Which of the following is NOT a universal logic gate?
a) NOT
b) AND
c) OR
d) NAND
Answer: b) AND
Explanation: NAND and NOR gates are universal; AND alone is not.

A P-type semiconductor is:
a) Positively charged
b) Negatively charged
c) Electrically neutral
d) Charged at high temperature only
Answer: c) Electrically neutral
Explanation: P-type semiconductors have equal positive acceptor ions and holes, remaining neutral.

At room temperature, the conduction band of a semiconductor is:
a) Completely empty
b) Partially filled
c) Completely filled
d) Same as valence band
Answer: b) Partially filled
Explanation: Thermal energy excites some electrons into the conduction band.

A diode is basically a:
a) Resistor
b) Conductor
c) Semiconductor device
d) Capacitor
Answer: c) Semiconductor device
Explanation: Diodes allow current flow in one direction using semiconductor material.

Doping a semiconductor with pentavalent impurities produces:
a) P-type semiconductor
b) N-type semiconductor
c) Insulator
d) Metal
Answer: b) N-type semiconductor
Explanation: Pentavalent atoms provide extra electrons, making N-type material.

In a forward-biased P-N junction diode, the depletion region:
a) Becomes wider
b) Disappears
c) Becomes thinner
d) Remains unchanged
Answer: c) Becomes thinner
Explanation: Forward bias reduces the depletion region allowing current flow.

Which device is used to stabilize voltage in electronic circuits?
a) Diode
b) Transistor
c) Zener diode
d) Capacitor
Answer: c) Zener diode
Explanation: Zener diodes maintain constant voltage across loads.

The output of an NPN transistor in active mode is controlled by:
a) Base current
b) Collector current
c) Emitter current
d) No current
Answer: a) Base current
Explanation: Small base current controls large collector current.

The typical energy gap of a semiconductor is approximately:
a) 10 eV
b) 1 eV
c) 5 eV
d) 0.1 eV
Answer: b) 1 eV
Explanation: Semiconductor energy gaps are typically around 1 electron volt.

Which of the following materials is commonly used as a semiconductor?
a) Copper
b) Germanium
c) Aluminium
d) Iron
Answer: b) Germanium
Explanation: Germanium is a standard semiconductor material.

In a half-wave rectifier, the output current is:
a) Alternating current
b) Direct current
c) Zero current
d) Pulsating DC
Answer: d) Pulsating DC
Explanation: Only one half of AC passes, producing pulsating DC.

The main advantage of using semiconductors in electronics is:
a) High conductivity
b) Control over conductivity by doping
c) Perfect insulators
d) No resistance
Answer: b) Control over conductivity by doping
Explanation: Conductivity can be precisely controlled by adding impurities.

An intrinsic semiconductor:
a) Has equal electrons and holes
b) Has only holes
c) Has only electrons
d) Has no charge carriers
Answer: a) Has equal electrons and holes
Explanation: Pure semiconductor has equal carrier concentrations.

The junction formed between P-type and N-type semiconductors is called:
a) Metal-semiconductor junction
b) P-N junction
c) Capacitor
d) Diode bridge
Answer: b) P-N junction
Explanation: P-N junction is the basic building block of semiconductor devices.

The process of adding impurities to a semiconductor is called:
a) Doping
b) Diffusion
c) Alloying
d) Annealing
Answer: a) Doping
Explanation: Doping introduces impurity atoms into semiconductors.

The transistor fundamentally has how many terminals?
a) One
b) Two
c) Three
d) Four
Answer: c) Three
Explanation: Emitter, base, and collector make the three terminals.

Which type of semiconductor has electrons as majority carriers?
a) Intrinsic
b) P-type
c) N-type
d) Metallic
Answer: c) N-type
Explanation: N-type semiconductors have electrons as majority carriers.

The resistance of a semiconductor:
a) Increases on heating
b) Decreases on heating
c) Remains constant
d) Fluctuates
Answer: b) Decreases on heating
Explanation: Heat excites electrons to conduction band reducing resistance.

The function of a transistor in an amplifier circuit is to:
a) Convert AC to DC
b) Increase signal strength
c) Rectify signals
d) Generate signals
Answer: b) Increase signal strength
Explanation: Transistors amplify weak signals.

Which device can act as a switch in electronic circuits?
a) Capacitor
b) Transistor
c) Transformer
d) Resistor
Answer: b) Transistor
Explanation: Transistors can switch current on and off rapidly.

The depletion region in a P-N junction contains:
a) Free electrons
b) Free holes
c) Immobile ions
d) Mobile charge carriers
Answer: c) Immobile ions
Explanation: Depletion region has fixed charged ions with no free carriers.

Light-emitting diodes (LEDs) convert:
a) Electrical energy to heat
b) Electrical energy to light
c) Light energy to electrical energy
d) Electrical energy to sound
Answer: b) Electrical energy to light
Explanation: LEDs produce light when current flows through them.