SSC JE 2012 Electrical question paper with solution

Thyrite is used widely in lightning arresters. It does not follow Ohm’s law, for each time the voltage is doubled the current increases 12.6 times. This means the resistance decreases as the current and voltage increase

Fixed charge for consumer = 12 x 100 = 1200 Rs

Running Charge = 1 x 4.5 x 15 x 365 = 24637.5 Rs

Annual bill = Running charge + fixed charge

= 24637.5 + 1200 = 36637.50

Glare is a visual sensation caused by excessive and uncontrolled brightness.Glare is caused by a significant ratio of luminance between the task (that which is being looked at) and the glare source.

Induction heating is the process of heating an electrically conducting object (usually a metal) by electromagnetic induction, through heat generated in the object by eddy currents. An important feature of the induction heating process is that the heat is generated inside the object itself via heat conduction.

Eddy current heating

This type of heating is also one of the forms of induction heating. Due to a high-frequency current ( 10 kHz to 400 kHz),  the conversion of electromechanical energy into heat takes place in the charge itself.

A resistance furnace is an electric furnace in which heat is generated by the conductor that offers resistance to the passage of a current through them. Temperature up to 3000°C can be obtained in the furnace chamber hence they are preferred for cremation.

There are mainly two functions of the choke coil

1.  Limit the current.
2. Produce high voltage across tube light.

Produces High voltage Across Tubelight

• Choke is nothing but the coil/ballast ( inductor) which is used to induce the high voltage across it. as we know that inductor has the property to induce high voltage for a brief period of time, this high voltage is required to ionize the gases in the starter.

The main reasons for an Electromechanical contactor or coil to ‘chatter’ is under voltage, an incorrect device (DC coil or no shading ring) or wrong/low frequency.

To eliminate this undesirable feature a shading coil is added. A shading coil usually takes the form of a single turn of heavy copper wire, or a copper ring, placed around one half of the end of the pole piece. With suitable adjustments of these copper shading bands, the maximum phase difference, Φ = 90°, is obtained between the fluxes electromagnets.

Magnetic blow-outs have been used in contactors, circuit breakers and controllers they are particularly used for low voltage alternating current. They extinguish the arc by means of a magnetic blast. It is limited to circuits up to 11 kV since air circuit breaker is used in low voltage, therefore, they are preferred for Air breaker circuit breaker.

Pitch factor is the ratio between the winding pitch and pole pitch

Pitch factor= Winding pitch/Pole pitch

In the case of full pitch winding, the winding pitch is equal to pole pitch. in other words, for a full pitch winding the pitch factor is equal to unity and the winding is known as “full pitch winding”.

Voltage in two parallel branches are same

V = Im(Rm + Rs + jXm)

V = Ish(Rsh + jXsh)

Im/Ish = (Rsh + jXsh)/(Rm + Rs + jXm)

This ratio should be independent of frequency. Performing rationalization and putting the imaginary part equal to zero as

For frequency Independency, the Imaginary part is zero

i.e., the shunt time constant should be equal to the meter time constant.