Electrical Engg (EEE) - MCQ Practice Questions

CMOS has virtually zero static power consumption because complementary transistors prevent direct paths from supply to ground in steady state.

Synchronizer circuits use cascaded flip-flops to provide settling time between asynchronous signal and sampling clock, reducing metastability risk.

The D flip-flop captures input D on clock edge and transfers it to output: Q(n+1) = D. This represents 'data' or 'delay' functionality.

Asynchronous circuits lack global clock, so multiple state variables can change simultaneously, causing race conditions and hazards if not carefully designed.

Combinational circuits produce outputs based solely on current inputs. Sequential circuits have memory elements (flip-flops) and outputs depend on input history.

Nyquist theorem states fs ≥ 2×fmax to avoid aliasing. Sampling below this rate causes frequency components to fold back and corrupt the signal.

Tristate logic provides high, low, and high-impedance states, enabling multiple devices to connect to a single bus by controlling which device actively drives the line.

Maximum frequency = 1/(4 × propagation delay) = 1/(4 × 10 ns) = 12.5 MHz. For ripple counters, the total delay is n × tpd.

For n input variables, truth table rows = 2^n. For 6 inputs: 2^6 = 64 rows.

Both static hazards (output glitches) and dynamic hazards (multiple transitions) can occur in combinational logic of counter design. Proper K-map grouping and implementation techniques are needed to minimize them.

A 3-to-8 decoder requires 8 output lines. Each output is active for one unique combination of 3 inputs, requiring 8 AND gates, each with 3 inputs (one for each input variable or its complement).

Mealy machines produce outputs based on both the current state and input variables, unlike Moore machines which depend only on the current state. This makes Mealy machines more efficient in detecting sequences.

Setup time is a manufacturer-specified parameter that varies by IC type and technology. At 100 MHz (10 ns period), typical setup times range from 2-5 ns, but exact requirements must be verified from the datasheet. General frequency calculation alone cannot determine setup time.

In a priority encoder with MSB having highest priority, when I7=1 (highest priority input), the output represents position 7, which is 111 in 3-bit binary. Lower priority inputs I5 and I3 are ignored.

The dielectric strength of air at standard conditions (1 atm, 25°C) is approximately $30\text{kV/cm}$. For a 1 cm gap, the breakdown voltage is $30\text{kV/cm}\times 1\text{cm}=30\text{kV}$. This is a fundamental reference value in high voltage engineering.

Paschen's law states that the breakdown voltage $V_b$ of a uniform-field gas gap is a function of the product $pd$, i.e., $V_b=f(pd)$. This is expressed as the Paschen curve, which shows a minimum breakdown voltage at an optimum $pd$ value. Both pressure and gap distance affect breakdown only through their product.

In a Marx generator, $n$ capacitors are charged in parallel (each to $V_0$) and then switched in series during discharge. The theoretical maximum output voltage is $n\cdot V_0$. In practice, the actual output is slightly less due to stray capacitances and resistive losses, but $n\cdot V_0$ is the ideal value.

According to IEC 60060-1, the standard lightning impulse waveform has a front time of $1.2\mu \text{s}$ and a time to half-value of $50\mu \text{s}$, denoted as $1.2/50\mu \text{s}$. The $8/20\mu \text{s}$ waveform is used for surge current testing, and $250/2500\mu \text{s}$ is the standard switching impulse.

At balance in the Schering bridge, the loss tangent (dissipation factor) of the test capacitor is given by $\tan \delta =\omega R_4{C}_4$, where $\omega =2\pi f$ is the angular frequency, $R_4$ is the variable resistance, and $C_4$ is the capacitance in the bridge arm. This relationship allows direct measurement of dielectric loss.

Corona onset occurs when the electric field at the surface of the conductor equals the critical ionization field of surrounding air, approximately $30\text{kV/cm}$ (or $3\text{MV/m}$) at standard atmospheric conditions (1 atm, 25°C). This is the point at which air molecules begin to ionize, causing partial discharge (corona). Temperature of the conductor or insulator rating are not the governing criteria.