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Question : Differentiate between LED's and PN junction diode? State the reason why cut in voltage is high for LED's?

Answer :

Light Emitting Diode is a PN diode but the difference between LED’s and PN junction diode is that material of PN diode is of Indirect Semiconductor (Si, Ge) material and material of LED is of direct semiconductor material (Ga, As).

However, Normal diodes are used in electric circuits as resisting semiconductors, where as LEDs  are specifically designed to produce light from the extra  energy generated by their resistance. The cut in voltage of LED is higher because LEDs are made up of material like GaAs or GaAsP which have more threshold voltage.


Question : How can we measure frequency without CRO?

Answer :

The frequency of any electrical signal can be measured by many devices, CRO is one of them. Other than CRO, Frequency Counter is one of the most popular examples.

The alternative tool for measuring periodic events is Spectrum analyzers (digital signal analyser).


Question : Why two ground pins are used in the 8086 pin diagram?

Answer :

The Pin + VCC is used to provide power supply to it and GND pin is used to earth the pin to prevent voltage breakdown in it.

Moreover, as the power consumption of chips increase, more ground pins are used to spread out the current and then each pin has a less current and hence lesser voltage drop.


Question :  How can you increase the range of a DC Voltmeter?

Answer :

Connect a resistance to the voltmeter in series connection to increase the total resistance and thus resulting in increase in the range of a DC voltmeter. 


Question : What happens when a voltmeter is connected in series connection in the circuit?

Answer :

The circuit resistance becomes too large when a voltmeter is connected in series with the circuit and consequently a very small current flows through the circuit. However, the instrument reads almost the same emf acting on it.


Question : Can we change ammeter to a voltmeter?  If yes, then how?

Answer :

An ammeter of low range can be transformed into a voltmeter by connecting a high resistance in series, provided that the current through series is within the range of the ammeter when connected across the voltage.


Question : Enlist the disadvantages of karnaugh maps?

Answer :

The K maps not necessarily fail for higher dimensions. The disadvantage is that it is very difficult to visualize for more than five variables. A 4 variable K-map is 2-D and easy to visualize. A 5 variable is three dimensional, but is still manageable from a visualization standpoint, because the 2 states of the 5th variable only require visually moving from one plane to the next, without moving in the x or y directions of either plane. Just getting equations correct with more than 5 variables is difficult 


Question : Explain the Kirk effect? How to eliminate Kirk Effect?  

Answer :

The Kirk effect happens at high current densities. This causes an increase in the transit time of a bipolar transistor. Charge density associated with current passing through the base-collector region is responsible for this effect. 

Kirk Effect can be eliminated by increasing the collector doping. Although, this increases the base-collector capacitance and the collector-base breakdown voltage decreases. Thus Kirk effect affects both power devices and RF.


Question : Explain the process to select switch based on application?

Answer :

The process for selecting a switch is given below:

  • First, we have to consider the needs of the end user.
  • Then examine the engineering constraints viz. load, contact materials and voltage; circuit type; mounting terminal type; etc.
  • Care must be taken while complying with certain standards, such as RoHS and other government regulations.
  • Determine the actuator type after ensuring the compliance with the applicable regulations
  • Finally, the selected switch must be reliable for the application.


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