AFCAT EKT Electrical Mock Test - 3 - AFCAT MCQ

A microwave based communication link has all the above mentioned advantage over any other lower frequency based communication system.

Directive gain, 
Now

The Avalanche breakdown happens if the reverse bias voltage is very high, then the velocity and associated kinetic energy of carriers increases to a point that impact will cause ionization process  to a point where a high avalanche current is established.

Filter removes higher frequency component of rectified cutout signal therefore filter reduces ripple present in the signal and which gives smaller ripple factor.

Transformer voltage comes into play in iron losses and the current is used to calculate copper losses. Thus the transformer ratings consist of both voltage and current and thus the ratings are expressed in KVA.

A laser makes monochromatic light of a single, very precise frequency and colour. The laser line is also very coherent as the crest of every wave is lined up with the crest of other waves.

Insulators are non-conducting material that prevents the leakage of electric current in unwanted directions. Thus it is used to provide electrical insulation.

The signal to quantization ratio of an n bit PCM system is
SNR = 6n + 1.8 dB
Thus, SNR increases as number of bits n increases.

• The degree to which an object conducts electricity is known as conductance
• It is calculated as the ratio of the current which flows to the potential difference present
• This is the reciprocal of the resistance and is measured in Siemens or mhos
• Resistance is measured in ohms

In under commutation, the commutation does not complete before the brush has moved from one commutator segment to the next. This leads to sparking at the trailing edge of the brush.

Dimensions of force is MLT^-2. Energy = Force × Distance. Dimensions of energy are ML²T^-2. Power is energy per unit time. The dimensions of power are ML²T^-3.

RC phase shift oscillator is used to invert the input for 180° phase difference. The single R-C network gives the 60° phase shift. Hence, we need three set of R-C network which have to be connected in cascade (series). The value of R and C can be chosen by the formula, 

When a positive voltage is applied to the N-type material and a negative voltage is applied to the P-type material, then a diode is connected in a reverse bias condition. In reserve bias the holes and electrons are attracted to the battery terminal and depletion region increased.

In an induction motor, the rotor copper losses are given as I²r₂, while the rotor input and rotor output are expressed as  and 

It is a majority carrier device. It is a semiconductor diode with a very fast switching action, but a low forward voltage drop. When a current flows through the diode there is a small voltage drop across the diode terminals. In a normal diode, the voltage drop is between 0.6 to 1.7 volts, while in a Schottky diode the voltage drop normally ranges between 0.15 and 0.45volts. This lower voltage drop provides higher switching speed and better system efficiency.
In Schottky diode, a semiconductor-metal junction is formed between a semiconductor and a metal, thus creating a Schottky barrier. The N-type semiconductor acts as a cathode and the metal side acts as the anode of the diode. The Schottky barrier diode is a unidirectional device conducting current flows only in one direction.

For x = r cos θ, y = r sin θ
We have x² + y² = r² 

The noise at the detector output of a DSB-SC demodulator is only the in-phase component of noise. The quadrature noise component is eliminated by the coherent detector.

The Friis transmission formula relating the received power P_r to transmitted power P_t is given by, 
Thus, from all the above statements, the only statement that is true is that the received power is directly proportional square of the wavelength of transmitted wave.

The power factor will be given as . It can be calculated as ratio of resistance to impedance. Thus, cosø = 12/15 = 0.8.

A NOR or an EX - NOR gate is one which gives the value one if and only if all operands have a value of zero and otherwise has a value of zero.

The linear variable differential transformer (LVDT) (also called just a differential transformer, linear variable displacement transformer, or linear variable displacement transducer) is a type of electrical transformer used for measuring linear displacement (position). Differential transformer is variable inductance transducer.

At high frequencies, such as microwave frequencies, transit time noise becomes a very significant concern.

The speed of electromagnetic waves in free space is equal to the velocity of light.

A PAM signal can be detected by using a low pass filter. The Low-pass filter for the PAM modulator is designed in such a way that the time constant of the filter matches with the time period of the modulating signal. Since 1KHz sine wave is used as modulating signal, the time constant of the low pass filter using the RC circuit is 1ms.

Order of the differential equation is the highest derivative in a differential equation. Hence the order is 2. 

The modulation system where different data bits are represented by differing phases is phase shift keying. Since there are four symbols, the phase shift keying is known as quadrature phase shift keying.

At cogging, the stator and rotor teeth get locked and rotor stops rotating after the locking.

The stator frame is the outermost part of the induction motor. It is made up of the cast iron and its main function is to provide mechanical support to the stator core. It is not designed to carry the stator flux.