AFCAT EKT Electrical Mock Test - 1 - AFCAT MCQ

In an ideal transformer, there are no no-load losses and magnetic leakage losses. Rest other things can be used in practical transformers also.

Dimension of magnetic flux density is MT^-2I^-1

Color in soap bubble is due to phenomenon of thin film interference. There is a thin film like structure formed between the outer and inner surface of the bubble, which reflects a spectrum of beautiful colors from its surface.

The given matrix is

The determinant is given as |A| = λ³ – 1               
If ⍴(A) is given as 2, then the determinant of A should be zero
⇒ |A| = 0 ⇒ λ³ – 1 = 0;
We get λ = 1  at which there are more than one 22 sub-matrices having non zero determinant
∴ value of λ is 1 for which rank of A is 2

The physical properties of electromagnetic waves can be determined from the spectroscopy experiment which detects the wavelengths of objects emitting these.

ECL - Emitter Coupled Logic circuit uses differential pair of transistors biased by constant current source coupled to emitter.
Depending on the logic the current flows from one transistor or the other, the total current drawn by the circuit remains same regardless of logic.
Since the current is constant during switching , hence unlike in CMOS or TTL no noise spikes occur during switching.

DAC has 10 bits, that means the total number of steps = 2¹⁰ - 1 = 1023
Resolution 

In a square law detector method a detector probe is moved along slot in transmission line and values of maximum and minimum voltage V_max, V_min are measured, on crystal detector (usually point contact or Schottky barrier diodes). 

RC is the time constant of a series resistance capacitance DC voltage circuit. The dimension of RC is same as that of time.

Op-Amp comparator circuit is used to compare the difference between voltage level of two inputs (inverting and non-inverting) and also determines which one is greater. It requires no feedback circuit.

The maximum power transfer theorem states that, to obtain maximum external power from a source with a finite internal resistance, the resistance of the load must equal the resistance of the source as viewed from its output terminals.
The efficiency is only 50% when maximum power transfer is achieved, but approaches 100% as the load resistance approaches infinity, though the total power level tends towards zero.

The working principle of pulse radar is that continuous pulses are transmitted and time is recorded until the pulse is received back by the radar. Based on this delay recorded, the range of target is estimated.

Spread spectrum uses a wide frequency band and allocates all resources to all simultaneous users, controlling the power transmitted by each to a minimum required to maintain a signal-to-noise ratio for the required level of performance. In this way a simple receiver will pass the signal as background noise making it harder to detect and jam

When impurities are added to other wise perfect crystals of semiconductors additional energy levels are created. In P-type semiconductor accepted impurities have one covalent bond empty which will easily accept a free electron from valence band due to thermal or optical excitation. The energy level is closer to valence band in P-type semiconductor.

Magnitude of resultant Forces F₁ and F₂ is:

F₁ and F₂ = P

In commutation, if reversal of current is completed during the short circuit time then the coil develops reactance voltage due to which sparking occurs at the brushes.

The value of Junction depletion capacitance is given by

Where A = Area of junction
W = width of Depletion region 

Hence 

The bandwidth requirement of a telephone channel is approximately 3 kHz.

Greater the stiffness of the material, more is the speed. Speed of sound in metallic solid will be higher than in a gas or liquid. Hence the velocity of sound will be least in distilled water.

Depending on the starting material and the type of MOSFET to be grown one of the above process can be used in CMOS fabrication.

LVDT works under the principle of mutual induction, and the displacement which is a non-electrical energy is converted into an electrical energy. LVDT consists of a cylindrical former where it is surrounded by one primary winding in the center of the former and the two secondary windings at the sides. The number of turns in both the secondary windings is equal, but they are opposite to each other, i.e., if the left secondary windings is in the clockwise direction, the right secondary windings will be in the anti-clockwise direction, hence the net output voltages will be the difference in voltages between the two secondary coil.

For number of quantisation levels, L = 128. The maximum quantisation error,  where Δ is step size. Now step size
Thus, maximum error, 
Hence, maximum error is 1/256 of the total amplitude range.

For stable feedback system, gain margin and phase margin both are positive.

Effective modulation index, 
We have 
Thus, 
In percentage, μ = 50%

P-i-N photodiodes contain layer of intrinsic semiconductor sandwiched between, P and N type semiconductors. The depletion region is contained entirely in the i-region.The thickness of intrinsic region can be adjusted to produce device with optimum sensitivity and frequency response.
Avalanche photo diodes arc reverse-biased p-n junction diodes that arc operated at voltages above breakdown voltage. They have higher power handling capacity.

The given integral is of the beta function. Hence it can be written as

Here n = 4, therefore the integral becomes

To get the dual of the given expression change OR to AND operator and AND to OR operator.

For a carrier signal,  the corresponding FM signal power is 
This is independent of depth of modulation. So output power of modulated FM is the same as unmodulated signal power.