SSC JE 2013 electrical question paper with solution

Answer 4. Under Voltage

Explanation:

Undervoltage occurs when the average voltage of a three-phase power system drops below the intended levels. Electromechanical devices, including three-phase motors and pumps, are designed to be operated at very specific voltage levels. If these devices are allowed to operate at reduced voltage levels they will draw higher currents which can damage the motor.

A three-phase monitor relay, with Undervoltage protection such as an electromechanical relay, is used for this purpose. The Undervoltage relay may either alarm or trip voltage-sensitive loads, such as induction motors, whenever the line voltage drops below the calibrated setting. For electromechanical relays, an instantaneous Undervoltage relay with its contacts connected in series with the time Undervoltage relay contacts may also be used to provide a fast reset time.

Answer. D

The given triangle output can be changed into the square output

The instantaneous value of capacitor current is

i(t) = cdv/dt

where C is the capacitance in farad

dv/dt = = instantaneous rate of voltage change(Volt/second)

For charging rate of voltage change is 10 and for discharging rate of voltage change is -11 therefore

Explanation:

• In a semiconductor, there is a bandgap and at absolute zero temperature, all the electrons are below the gap, and thus not available for conduction.
• At finite temperature, some electrons are thermally excited into the conduction band, and thus you get conduction when an electric field is applied. As the temperature is increased covalent bonds breaks and more electron-hole pairs are available for conduction. Thus conductivity increases and resistivity, the reciprocal of conductivity decreases.

Answer 3. 100 c/s

Explanation:

Frequency of instantaneous power consumed = 2f = 2 x 50 = 100 c/s

Explanation:

The SI unit of charge, the coulomb, “is the quantity of electricity carried in 1 second by a current of 1 ampere

Explanation: 

Since capacitor are connected in parallel therefore

PF = PF1 + PF2 / 2

= 0.01 + 0.02 /2

= 0.015

Answer 4. 1.5Ω

Explanation:

Current through voltmeter

Iv = V/R = 4/50000 = 8 x  10^-5 A

Dc supply voltage Vdc = 120 V

Then the value of unknown resistance is given as

R = V/I

R = 120/8 x  10^-5  = 1.5 MΩ

Explanation:

• There are mainly two functions of the choke coil
  1.  Limit the current.
  2. Produce high voltage across the tube light.

Limit the current

• In a gas discharge, such as a fluorescent lamp, current causes resistance to decrease. This is because as more electrons and ions flow through a particular area, they bump into more atoms, which frees up electrons, creating more charged particles.
• In this way, the current will climb on its own in a gas discharge, as long as there is an adequate voltage (and household AC current has a lot of voltage).
• If the current in a fluorescent light isn’t controlled, it can blow out the various electrical components.

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.

Explanation:

• The 100W lamp will fail first, Although the voltage across the 100 w lamp will be higher (293V), it will fail because of the effective current (0.489A) which is more than the 100 w lamp’s normal current (0.4A).
• An increase in current causes more heat and the heating element will fail.

Explanation: