Free Electronics and Devices MCQs with Answers

• A. Ri=∞ ,A=∞ ,R0=0
• B. Ri=0 ,A=∞ ,R0=0
• C. Ri=∞ ,A=∞ ,R0=∞
• D. Ri=0 ,A=∞ ,R0=∞

Explanation: An ideal op-amp draws no input current, has infinite open-loop gain, and has zero output resistance.

• A. Not need an input resistor
• B. Be virtual ground
• C. Have high reverse current
• D. Not invert the signal

Explanation: With the non-inverting terminal grounded and negative feedback present, the virtual-short rule forces the inverting terminal to…

• A. Less than one
• B. Greater than one
• C. Of zero
• D. Equal to one

Explanation: A non-inverting amplifier has gain Av = 1 + Rf/R1, so with a normal positive feedback resistor its gain is greater than unity.

• A. The ratio of the input resistance to feedback resistance
• B. The open-loop voltage gain
• C. The feedback resistance divided by the input resistance
• D. The input resistance

Explanation: For an inverting amplifier, the closed-loop gain is Av = −Rf/Ri, so its magnitude is the feedback resistance divided by the input…

• A. 1.273kHz
• B. 12.73kHz
• C. 127.3 kHz
• D. 127.3 Hz

Explanation: Using fc = 1/(2πRC), with R = 2.5 kΩ and C = 0.05 μF, gives approximately 1,273 Hz or 1.273 kHz.

• A. from south pole to north pole
• B. from north pole to south pole
• C. from one end of the magnet to another
• D. none of the above

Explanation: Outside a magnet, magnetic field lines conventionally run from the north pole to the south pole; inside the magnet they complete the path…

• A. which is a good conductor
• B. which is a bad conductor
• C. which is a strong magnet
• D. through which the magnetic lines of force can pass very easily

Explanation: Permeability indicates how readily a material allows magnetic flux to pass through it.

• A. iron
• B. copper
• C. aluminium
• D. moving charges

Explanation: A moving electric charge produces a magnetic field, as shown by the magnetic field surrounding a current-carrying conductor.

• A. weak magnets
• B. temporary magnets
• C. permanent magnets
• D. none of the above

Explanation: Low retentivity means the material loses most of its magnetism when the magnetising force is removed.

• A. field strength
• B. inductance
• C. flux density
• D. flux

Explanation: The tesla is the SI unit of magnetic flux density, with 1 T equal to 1 weber per square metre. Magnetic flux itself is measured in webers.

• A. paramagnetic
• B. diamagnetic
• C. ferromagnetic
• D. none of the above

Explanation: Ferrites are ceramic magnetic materials containing iron oxides and generally exhibit ferrimagnetic behaviour, which is classified under…

• A. The electric intensity is a vector quantity
• B. The electric field intensity at a point is numerically equal to the force exerted upon a charge placed at that point
• C. An electric field is defined as a point in space at which an electric charge would experience a force
• D. Unit field intensity in the exertion of a force of one newton on a charge of one coulomb

Explanation: Electric field intensity is force per unit charge, E = F/q, so it equals the force only when the charge is 1 coulomb.

• A. KT3 and 1CT6
• B. 1CT3 and 1CT7
• C. KT4 and KT8
• D. 10″2 and KT5

Explanation: Paramagnetic materials have a small positive susceptibility, commonly of the order of 10^-3 to 10^-6.

• A. Diamagnetic materials
• B. Ferrimagnetic materials
• C. Antiferromagnetic materials
• D. Antiferrimagnetic materials

Explanation: In an antiferromagnetic material, neighboring atomic magnetic moments are equal and oppositely aligned, so they cancel and produce zero…

• A. low coercivity
• B. high susceptibility
• C. both of the above
• D. none of the above

Explanation: An electromagnet should magnetize strongly when energized and lose its magnetism readily when the current is removed.

• A. heating
• B. hammering
• C. by inductive action of another magnet
• D. by all above methods

Explanation: Heating and hammering disturb the aligned magnetic domains, while a strong opposing or inductive magnetic field can also reduce their…

• A. Paper capacitor
• B. Ceramic capacitor
• C. Electrolytic capacitor
• D. Any-of the above

Explanation: An electrolytic capacitor is polarized, so connecting it with reverse polarity can cause excessive leakage current, heating, gas…

• A. Air
• B. Paper
• C. Mica
• D. Electrolytic

Explanation: Electrolytic capacitors are polarized and therefore marked with positive and negative terminals.

• A. zero
• B. proportional to applied voltage
• C. proportional to value of capacitance
• D. both (B) and (C) above

Explanation: A pure capacitor stores and returns energy but does not consume average real power, because its current leads voltage by 90°.

• A. two insulators separated by a conductor
• B. two conductors separated by an insulator
• C. two insulators only
• D. two conductors only

Explanation: A capacitor is formed by two conducting plates separated by an insulating dielectric.