RRB JE Electronics Engineering — Solved Practice Question Bank

Q: Convert binary 1011 to decimal. Sol: 1×2³ + 0×2² + 1×2¹ + 1×2⁰ = 8+0+2+1 = 11. Q: Which flip-flop has no invalid/forbidden input state, unlike the SR flip-flop? Sol: JK flip-flop — when both J and K are 1, it toggles output instead of entering an undefined state (which is what happens in an SR flip-flop when both inputs are 1). Q: Name a "universal" logic gate that can implement any Boolean function alone. Sol: NAND (or NOR) — either one alone is sufficient to construct AND, OR, and NOT gates, hence any logic function.

Q: Which transistor configuration gives 180° phase inversion between input and output? Sol: Common Emitter (CE) configuration. Q: What is the ripple frequency of a full-wave rectifier fed by a 50 Hz AC supply? Sol: 100 Hz — full-wave rectification produces two output pulses per input cycle, doubling the ripple frequency. Q: What is a Zener diode primarily used for? Sol: Voltage regulation — it is operated deliberately in reverse breakdown, maintaining a nearly constant voltage across it over a range of currents.

Q: Why is FM generally more noise-resistant than AM? Sol: Because most electrical noise affects signal amplitude, and FM carries information in frequency variations rather than amplitude — an amplitude limiter can remove noise without affecting the FM signal. Q: A signal has a maximum frequency of 4 kHz. What is the minimum sampling rate to avoid aliasing? Sol: By the Nyquist theorem, minimum sampling rate = 2 × 4kHz = 8 kHz. Q: What does the Program Counter in a microprocessor hold? Sol: The address of the next instruction to be fetched from memory.