SSC JE electrical question paper 2019 with solution SET-2

Answer.3. Induction type

Explanation:-

Creeping Error

The slow but continuous rotation of the energy meter (Induction type) when only the pressure coil is excited and no current is flowing through the current coil is called creeping. This error may be due to excessive friction compensation, excessive voltage supply, stray magnetic field, etc.

In order to prevent creeping at no-load, two holes of the same radius are drilled in the disc on the opposite side of the spindle.

Answer.2. Generator

Explanation:-

INDUCED E.M.F.

The e.m.f. is induced in the conductor in two ways.

1. Dynamically induced e.m.f:- In Dynamically induced e.m.f., the conductor will move in the magnetic field and flux will be non-varying.
2. Statically induced e.m.f:- In Statically induced e.m.f., the conductor will be stationary and the flux will be varying.

DC Generator

A DC generator is a dynamic DC machine, which generates electrical energy from mechanical energy. The emf induced is called dynamically induced emf. It operates on the principle of Faraday’s law of electromagnetic induction, which states that whenever a current-carrying conductor cuts the magnetic flux, a dynamically induced emf is generated. Its magnitude depends on the rate of change of magnetic flux linked with the conductor. If the conductor is connected to a closed circuit, then a current will flow through it. The basic elements required in a DC generator to generate a dynamically induced emf are:

1. A steady magnetic field
2. A current-carrying conductor
3. Relative motion between the conductor and magnetic field

Answer.3. Eureka

Explanation:-

• The melting point of Eureka is 1221 to 1300 °C
• The melting point of Kanthal is 1,425 °C
• The melting point of Nichrome is 1400 °C
• The melting point of Graphite is 3,600°C

Hence Eureka has the least range of temperature.

Answer.4. Is equal to zero

Explanation:-

Two coils are said to be magnetically coupled if full or part of flux produced by one coil links with the other coil. If L₁ and L₂ are the self inductances of the two coils and M is the mutual inductance between the coils, then the coefficient of coupling k is given by

$M = \dfrac{K}{{\sqrt {{L_1}{L_2}} }}$

⇒ When there is no mutual flux between two coils, they are said to be magnetically isolated. In this case. k = 0 and M = 0.

⇒ If the entire flux of one coil links with the other then the mutual inductance between the two coils is maximum. In that case, k is equal to 1. Therefore,

$M = \sqrt {{L_1}{L_2}}$

Answer.4. 6

Explanation:-

Indian Electricity Rules specify that the maximum load on a light/fan sub-circuit should not exceed 800 watts and the number of points should be limited to 10.

Hence for light load number of sub-circuit = 3000/800 = 3.75 = 4

Indian Electricity Rules specify that the maximum load on a power sub-circuit should not exceed 3000 watts and the number of outlets should be limited to two.

For the power sub-circuit load number of sub-circuit = 6000/3000 = 2

Total subcircuit = 4 + 2 = 6

Answer.1. Turbine

Explanation:-

Boiler – Boiler is an equipment to produce steam. Thermal energy released by the combustion of fuel is transferred to water, which vaporizes and gets converted into steam at the desired temperature and pressure.

Steam turbine – High pressure superheated steam is fed to the steam turbine which causes turbine blades to rotate. The energy in the steam is converted into mechanical energy in the steam turbine which acts as the prime mover. The pressure and temperature of the steam fall to a lower value and it expands in volume as it passes through the turbine. The expanded low-pressure steam is exhausted in the condenser.

Generator – It is coupled with the turbine rotor and converts the mechanical energy of the turbine to the electrical energy.

Condenser – Condenser is a heat exchanger in which cooling water is circulated through the tubes. The exhaust steam from the turbine enters the condenser where it is cooled and converted to condensate (water).

Answer.1. Capacitor-start, Capacitor-run

Explanation:-

Capacitor-start, Capacitor-run type of motor is designed to operate with the start winding and it’s series capacitor permanently connected to the supply. lt has two capacitors connected in parallel in the start winding circuit for starting purposes. The running capacitor is employed to correct the power factor. As a result, this motor has a higher starting torque as well as a higher efficiency. These motors are employed in sizes ranging from 375 W to 7.5 kW.  The power factor of these motor is upto 80% to 100%.

Answer.3. 10 V

Explanation:-

Voltage Scale Span of  instrument = V_max − V_min

Given

V_max = 5 V

V_min = −5V

Span = 5 −(−5) = 10 V

Answer.1. Always less than the average speed

Explanation:-

Average speed:- The distance covered between two stops divided by the actual time of the run is known as average speed.

Average speed = (Distance between stops)/(Actual time of run)

Schedule speed:- It is defined as the ratio of distance covered between two stops and the total time of run including the time of the stop.

Schedule speed = (Distance between stops) /(Actual time of run + Stop time)

This shows that schedule speed is always smaller than the average speed. The difference is large in the case of urban and suburban services and is negligibly small in the case of main-line service.

Answer.1. Always less than one

Explanation:-

The slip of the induction motor is defined as the ratio of the difference between the synchronous speed (N_s) and the actual speed of rotor i.e. motor (N) to the synchronous speed (Ns).

$s = \dfrac{{{N_s} – N}}{{{N_s}}}$

In terms of slip, the actual speed of the motor (N) can be expressed as

N = N_s(1 − s)

At start, the motor is at rest and hence its speed N is zero.

s = 1 ( start)

This is the maximum value of slip s possible for the induction motor which occurs at start. While s = 0 gives us N = N. which is not possible for an induction motor. So slip of the induction motor cannot be zero under any circumstances.

Practically motor operates in the slip range of 0.01 to 0.05 i.e. 1 % to 5 %. The slip corresponding to the full load speed of the motor is called full load slip.