Interview Questions: ECE (basic-2)

Some electronics and communication engineering basic skill topics and answers are given here:

EM waves are reflected by perfect conductors!

This is the reason why your data connection becomes slow or calls easily get disconnected while travelling in a train, lift or you are near to a big metallic body.

A signal is 'active low or high' 

In digital circuits when: A signal is 'active low' means that signal will be performing its function when its logic level is 0. A signal is 'active high' means that signal will be performing its function when its logic level is 1.

Transformer secondary winding voltage

Each coil loop of the transformer secondary produces a voltage by means of electromagnetic induction to primary winding.  As the secondary winding loops are all in series or one after one and voltages in series add, the larger number of loops produce large voltage and less number of loops produce less voltage. A easy way to understand step-up and step-down mechanism.

Flash memory

Flash memory is an electronic (solid-state) non-volatile computer storage medium that can be electrically erased and reprogrammed. Data on flash memory(thumb/pen drives and SD cards)  is erased through quantum tunneling. The most common type of flash memory in pen/thumb drives is NAND flash Flash memory which uses floating gate transistors Floating-gate MOSFET.

SEA-ME-WE 4

This stands for South East Asia–Middle East–Western Europe 4. Our entire internet is based on undersea fiber optic cables such as the SEA-ME-WE systems

Pen-drive 

If your pen drive uses FAT32 file system you cannot transfer a single file of size 4GB at a time, however you can convert the file system to NTFS and transfer a file of any size.

Mobile vibration

It's because of small dc motor. The motor that makes a phone vibrates is a stepper motor.

Music player

That what we see on our music player when we play a song is actually representation of Frequency spectra of a Tone-Frequency modulated wave! It's not there just because it looks good.

Brewster angle

The Brewster angle is the angle at which no reflection occurs in the medium of origin.

Mobile adapter

Mobile batteries require around 3.7-4.2 volts (200kHz) but our house is supplied at 230V (50kHz)  So we need a step down transformer in order to charge our mobile, which is present inside our charger. 

Did you ever notice gravel beneath around large transformers?

​​​​The main reason for this practice is actually "snakes".  Large transformers produce substantial vibrations due to magneto-striction which get transmitted to ground. Due to this effect the transformers placed on solid ground attract snakes. To prevent this, transformers are surrounded by gravel which prevents snakes from coming near it.

Shockwave

The shockwave during rain has a voltage as high as 50k–80k or even 1Lakh Volts. The ground has potential of 0 Volts. Thus there is a huge potential difference between cloud and ground and thus this makes even air as conductive material. By nature electric current follows the shortest and simplest path to flow and thus it flows through whatever taller conductive material present around to reach upto the ground. That’s why in urban areas most of the shockwaves fall on industrial chimneys or coconut trees which attain a great height in the surroundings. That’s why one shouldn’t walk around in an open park or field or stream through water bodies during heavy lightining.

The height at which a wire is suspended is related to the voltage it has.

The inter-district transmission lines carrying around 33,000 V are placed the highest. They're usually seen near a power house (regional distribution centres) and are quite thick. The next in height are the 11,000 V lines, placed at about 23-26 ft. They supply high electricity to local transformers which finally step down the voltage to 230 V (or 110 V in some places like America and Canada).At the lowest height are the 230 V lines, from which the service drops are made. 11000 V is stepped down to 400 V (Phase to Phase). There are 3 wires, carrying 3 different phases of electricity. Any one of the three phases and a neutral is supplied to the house, powering the appliances at 230 volts.

Electric bulb blinking

In AC power, the direction of the current flowing is continuously changing. filament bulb only glows on one direction of power flow.  So, the bulb continuously blinks. Human eyes can't make out that it is blinking because the frequency is 50 times per second or 50hz.

Flow of current

Current does not flow from positive to negative or vice versa, it flows in a continuous loop. By convention, from Ben Franklin, current is defined to flow from negative to positive inside a battery or power supply, and from positive to negative in the circuit outside a power supply.  Current is not really the movement of electrons, they actually move quite slowly. The electrons in the electrical wire going to your blow dryer travel at about 1 inch per minute. The electrical current flows at close to the speed of light.