SSC JE electrical question paper 2019 with solution SET-2

Answer.1. Sodium Vapor Lamps

Explanation:- 

The most common type of floodlight is the metal-halide lamp, which emits a bright white light (typically 75-100 lumens/Watt). Sodium-vapor lamps are also commonly used for sporting events because they imitate daylight conditions, and colors appear natural.

They have a very high lumen-to-watt ratio (typically 80-140 lumens/Watt), making them a cost-effective choice when certain lux levels must be provided.

Answer.2. Larger diameter, shorter axial length

Explanation:- 

The rotor of the synchronous machine carries a field winding that is supplied with d.c. through two slip rings by a separate d.c. source. Synchronous Rotor construction is of two types, namely :

1. Salient (or projections) pole type.
2. Cylindrical type (or non-salient pole type)

Salient-pole rotor:-

• In this type, salient poles are mounted on a large circular steel frame which is fixed to the shaft of the alternator.
• The rotors of salient-pole rotor machines have concentrated winding on the poles and a nonuniform air gap.
• Salient pole generators have a large number of poles. sometimes as many as 50, and operate at lower speeds.
• The synchronous generators in hydroelectric power stations are of the salient pole type and are driven by water turbines.
• The rotors are shorter axial length but have a large diameter.

Answer.3. 2 meters

Explanation:- 

Candle Power of lamp = 60 CP

Illumination of lamp = 15 lux

Distance(D) = ? meters

Illumination of lamp = (candle power)/(distance)²

(D)² = candle power/Illumination of lamp

(D)² = 60/15 =4

D = √4

D = 2

Answer.1. XOR is a derived gate

Explanation:- 

Basic logic gates: Basic logic gates are the building blocks of digital circuits that perform logical operations such as AND, OR, and NOT, on the binary inputs.  Basic gates are mainly used in the fabrication of digital systems and are called integrated circuits (ICs).

Derived logic gates: Derived logic gates arc those logic gates that perform logical operations on the binary inputs with the help of two or more basic logic gates. A combination of AND, OR, and NOT are called derived gates. NAND, NOR, XOR, and XNOR are such a combination of AND, OR, and NOT gates.

Exclusive OR (XOR) Gate

A gate that identifies the odd number of 1’s in the combination of the inputs is called the XOR gate. It is a functional combination of NOT, AND, and OR gates.

Answer.4. Air friction damping

Explanation:-

Air friction Damping: An air friction damping device is usually provided with moving iron instruments such as voltmeters and ammeters.

In this device, a light aluminum vane is attached to a spindle as shown in Fig. and this vane is free to move in a fixed air chamber known as a sector. When the pointer deflects, the vane in the sector also moves. The air in the sector produces friction in the movement of the vane and thus necessary damping torque is obtained.

Eddy Current Damping: It is used in a strong operating field e.g., PMMC (Permanent Magnet Moving Coil instrument) type.

Fluid Friction Damping: Used in high voltage measurement. Used in the vertically mounted instrument. e.g., Electrostatic type instrument.

Answer.1. 0.15 H

Explanation:-

The combined inductance of two coils connected in series

L = L₁ + L₂ + 2M

In series adding case

L₁ + L₂ + 2M = 0.6 H ——–(1)

In series opposing case

L₁ + L₂ − 2M = 0.1 H ——–(2)

Subtracting eqn (2) from eqn (1) we get

4M = 0.5 H

M = 0.125 H

Let L₁ = 0.2 H (since the coil when isolated, its self-inductance is 0.2 H)

Putting the value of  M &  L₁ in equation (2)

0.2 + L₂ + 2 ×0.125 = 0.06

0.2 + L₂  = 0.35

L₂  = 0.15 H

Answer.1. Single-phase induction motor

Explanation:-

The efficiency and power factor of single-phase motors are usually low. Thus at full-load a 186 W motor (1/4 hp) has efficiency and poor factor of about 60 percent. For the same size, the single-phase induction motors develop about 50% of the output as that of three-phase induction motors. The starting torque is also low for asynchronous motors / single phase induction motor.

The low power factor is mainly due to the large magnetizing current, which ranges, between 70 percent and 90 percent of full-load current. Consequently, even at no-load these motors have a substantial temperature rise. The power factor of 3-phase motors is of the order of 0.85 lagging, whereas it is 0.55 to 0.6 for single-phase motors.

The relatively low efficiency and power factor of single-phase induction motors is a consequence of their fractional horsepower ratings. The efficiency of 3-phase motors is quite high of the order of 80 to 90 %, while single-phase motors hardly work with an efficiency of 55 to 60 %.

Answer.4. 50 A

Explanation:-

Given

Power (P) = 20 kW = 20 × 10³ W

Voltage (V) = 200 V

P = VI = I = P/V

I = (20 × 10³)/200

I = 100A

For wave wound No. of Parallel Path = 2

Current in Each parallel Path for wave wound

I = 100/2 = 50 A

Answer.2. 0011

Explanation:-

The excess-3 code for a given decimal number is determined by adding ‘3’ or “0011” to each decimal digit in the given number.

Addition

The excess-3 code can be very effectively used to perform the addition of BCD numbers. The steps to be followed for excess-3 addition of BCD numbers are as follows:

1. The given BCD numbers are written in excess-3 form by adding ‘0011’ to each of the four-bit groups.
2. The two numbers are then added using the basic laws of binary addition.
3. Add ‘0011’ to all those four-bit groups that produce a carry, and subtract ‘0011’ from all those four-bit groups that do not produce a carry during addition.
4. The result thus obtained is in excess-3 form.

Subtraction

The subtraction of BCD numbers using the excess-3 code is similar to the addition process discussed above. The steps to be followed for excess-3 subtraction of BCD numbers are as follows:

1. Express both minuend and subtrahend in excess-3 code.
2. Perform subtraction following the basic laws of binary subtraction.
3. Subtract ‘0011’ from each invalid BCD four-bit group in the answer.
4. Subtract ‘0011’ from each BCD four-bit group in the answer if the subtraction operation of the relevant four-bit groups required a borrow from the next higher adjacent four-bit group.
5. Add ‘0011’ to the remaining four-bit groups, if any, in the result. 6. This gives the result in the excess-3 code.

Answer.1. R_L

Explanation:-

The maximum power transfer theorem states that the DC voltage source will deliver maximum power to the variable-load resistor only when the load resistance is equal to the source resistance. Similarly, this theorem states that the AC voltage source will deliver maximum power to the variable complex load only when the load impedance is equal to the complex conjugate of the source impedance.

Hence when R_i = R_L the transfer of power will be maximum.