📡 Electronics and Communication Engineering (ECE) Solved MCQs with Answers

Practice 406 approved 📡 Electronics and Communication Engineering (ECE) questions with verified answers from the 🛠️ Engineering Essentials subject for Pakistan exams.

406 solved MCQs

For a 400 kHz transmission line having L = 0.5 mH/km, C = 0.08 mF and negligible R and G, the value of propagation constant P will beAnswer: 15.9 radians/km The Depth of penetration of EM wave in medium having conductivity σ at a frequency of 1 MHz is 25 cm. The depth of penetration at a frequency of 4 MHz will beAnswer: 12.50 cm What is the characteristic impedance at 10 MHz?Answer: 547.7 Ω Calculate wave impedance for TE modeAnswer: 629 Ω A transmission line is feeding 1 watt of power to a horn antenna having a gain of 10 dB. The antenna is matched to the transmission line. The total power radiated by the horn antenna into the free space isAnswer: 10 watts A parallel polarized wave is incident from air into paraffin having relative permittivity 3, the value of its Brewster angle isAnswer: 60° The radiation resistance of a λ/16 wire dipole in free space will be nearlyAnswer: 3 Ω Find the noise factor for an antenna at 27°C with equivalent noise temperature 30°KAnswer: 1.1 To increase Q factor of a coil, the wire should beAnswer: thick An ammeter of 0-25 A range has a guaranteed accuracy of 1% of full scale reading. The current measured is 5 A. The limiting error isAnswer: 5% The coil of a moving iron instrument has a resistance of 500 Ω and an inductance of 1 H. It reads 250 V when a 250 V dc is applied. If series resistance is 2000 Ω, its reading when fed by 250 V, 50 Hz ac will beAnswer: 248 V In 3 phase power measurement by two wattmeter method, the reading of one wattmeter is zero. The power factor of load isAnswer: 0.5 In a CRO which of the following is not a part of electron gunAnswer: X - Y plates Which of the following voltmeters would you use for measuring voltage across 20 kΩ resistance?Answer: Voltmeter having sensitivity of 10 kW/V A single phase energy meter has the rating 1200 resolutions/ kWh. If a 500 W electric gadget is used for 4 hours, the energy meter will makeAnswer: 2400 revolutions Assertion (A): De sauty's bridge is suitable only for pure capacitor. Reason (R): Capacitors are mostly perfect.Answer: A is true R is false In which of the transformer is the secondary nearly short circuited under normal operating conditions?Answer: CT A moving coil instrument has a resistance of 0.6 Ω and full scale deflection at 0.1 A. To convert it into an ammeter of 0-15 A range, the resistance of shunt should beAnswer: 0.004 Ω A piezoelectric force transducer has a charge sensitivity of 20 pC/N. It is connected to a charge amplifier and overall gain of transducer and amplifier is 50 mV/N. The gain of amplifier isAnswer: 2.5 mV/pC An LVDT is used to measure displacement. The LVDT feeds a Voltmeter of 0-5 V range through a 250 gain amplifier. For a displacement 0.5 mm the output of LVDT is 2 mV. The sensitivity of instrument isAnswer: 1 V/mm Assertion (A): When a wattmeter is used for low impedance loads, the pressure coil is connected across the load. Reason (R): A wattmeter measures apparent power.Answer: A is true R is false As per BIS there are 6 accuracy classes of instruments.Answer: False In a ballistic galvanometer, a charge of 100 μC gives a first swing of 25°. The charge required to cause first swing of 50° isAnswer: 400 μC In a strain measuring device using a strain gauge, the output quantity isAnswer: voltage The Lissajous pattern observed on screen of CRO is a straight line inclined at 45° to x axis. If X-plate input is 2 sin ωt, the Y-plate input isAnswer: 2 sin ωt The angle δ for a mica capacitor is aboutAnswer: 1° A digital voltmeter has a read out range from 0 to 999 counts. If the full scale reading is 9.999 V, the resolution isAnswer: 1 mV Consider the following statements: In a differential amplifier using JFET, the differential output offset is due to 1. mismatch between FET parameters 2. difference in values of resistances used in circuit 3. variation in supply voltage. Of the statements, the correct statements areAnswer: 1 and 2 A meter with a resistance of 100 Ω and a full scale deflection of current of 1 mA is to be converted into voltmeter of 0 - 5 V range. The multiplier resistance should beAnswer: 4900 Ω The household energy meter isAnswer: integrating instrument