📡 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

The drift velocity of electrons isAnswer: very small as compared to speed of light Wave A = 100 sin ωt and wave B = 100 cos ωt. ThenAnswer: rms values of the two waves are equal A series RC circuit has R = 5 Ω and C = 10 μF. The current in the circuit is 5 sin 20000t. The applied voltage isAnswer: 25√2 sin (20000t - 45°) A capacitor stores 0.15C at 5 V. Its capacitance isAnswer: 0.03 F A 0.5 μF capacitor is connected across a 10 V battery. After a long time, the circuit current and voltage across capacitor will beAnswer: 0 A and 10 V Which of the following pairs are correctly matched? 1. Brune's realisation : realisation with ideal transformer. 2. Cauer realisation : ladder realisation. 3. Bott Duffin realisation : with non ideal transformer. Select the answer using the following codes:Answer: 1 and 2 The synthesis of minimum function was suggested byAnswer: O'Brune A 3 phase balanced supply feeds 3 phase unbalanced load. Power supplied to the load can be measured by using 1. 2 wattmeter 2. one wattmeter 3. 3 wattmeter Which of the above statements is correct?Answer: 1 and 3 Which of the following is correct for a driving point functions?Answer: The real parts of all poles and zeros must be negative or zero The impedance of an RC series circuit is 12 Ω at f= 50 Hz. At f= 200 Hz, the impedance will beAnswer: more than 3 Ω but less than 12 Ω A current is flowing through a conductor with non-uniform area of cross-section. ThenAnswer: current will be the same but current density will be different at different cross-sections. The electrical energy required to heat a bucket of water to a certain temperature is 2 kWh. If heat losses, are 25%, the energy input isAnswer: 2.67 kWh The current rating of a cable depends onAnswer: diameter of cable In an ac circuit, the maximum and minimum values of power factor can beAnswer: 1 and 0 A two branch parallel circuit has a 20 Ω resistance and 1 H inductance in one branch and a 100 μF capacitor in the second branch. It is fed from 100 V ac supply, at resonance, the input impedance of the circuit isAnswer: 500 Ω As compared to the number of network elements in Brune synthesis, the number of network elements Bott-and Duffin in realization isAnswer: more A sinusoidal voltage has peak to peak value of 100 V. The rms value isAnswer: 35.35 V A capacitor is needed for an ac circuit of 230 V, 50 Hz the peak voltage rating of the capacitor should beAnswer: √2 x 230V A broadside array consisting of 200 cm wavelength with 10 half-wave dipole spacing 10 cm. And if each array element feeding with 1 amp. current and operating at same frequency then find the half power beamwidthAnswer: 2° A broadside array operating at 100 cm wavelength consist of 4 half-wave dipoles spaced 50 cm apart. Each element carries radio frequency current in the same phase and of magnitude 0.5 A. The radiated power will beAnswer: 196 W The input impedance of short-circuited line of length l where λ/4 < l < λ/2, isAnswer: capacitive A wave is propagated in a waveguide at frequency of 9 GHz and separation is 2 cm between walls find cut off wavelength for dominant mode.Answer: 4 cm Find the radiation resistance of an antenna of length λ/10 meter?Answer: 7.8 Ω The phase angle corresponding to λ/4 in a standing-wave pattern isAnswer: 90° A hollow rectangular waveguide has dimensions a = 2b. Calculate the amount of attenuation, if the frequency is 3 GHz, and b = 1 cm.Answer: 47.33 A (75 - j 40) W load is connected to a co-axial line of z0 = 75ω at 6 MHz. The load matching on the line can be accomplished by connectingAnswer: an inductance at the load A plane electromagnetic wave travels in dielectric medium of relative permittivity 9. Relative to free space, the velocity of propagation in the dielectric isAnswer: reduced by a factor of 1/3 Consider a loss less antenna with a directive gain of + 6 dB. If 1 mW of power is fed to it the total power radiated by the antenna will beAnswer: 4 mW Which of the following should dominant wave have?Answer: Lowest cut off frequency Calculate the wave impedance for TM mode in rectangular waveguide for dominant mode at 3 GHz havingAnswer: 226 Ω