SSC JE electrical 2019 question paper with solution SET-1

Answer.1. µ

Explanation:-

When two solid surfaces are brought into contact, a finite normal force is needed to pull the two solids apart. This force is known as the force of adhesion or simply adhesion.

The coefficient of adhesion () defined as the ratio of tractive effort required to propel the wheel of a locomotive to its adhesive weight. Adhesion traction is the friction between the drive wheels and the steel rail.

µ = F_t/W

Where

F_t = Tractive effort

W = Adhesive Weight

Answer.4. 1-phase induction motors

Explanation:-

Split-phase, capacitor, and shaded-pole single-phase motors classified as single phase motor.

The single-phase motor with a single winding is not self-starting, because if the single winding is fed with a.c., it simply produces a “pulsating field” which rises and falls with the alternating current, and this type of field produces no torque in the rotor.

Answer.3. A.B

Explanation:-

The circuit shown in the question is an AND GATE. In an AND gate has two or more inputs but it has only one output. An input signal applied to a gate has only two stable states, either 1 (HIGH) or 0 (LOW). In AND gate for any input A&B the output is A.B.

Answer.1. 4H

Explanation:-

Mutual inductance between the two coils is K = √L₁.L₂

K = √2 × 8

k = √16

k = 4 H

Answer.1. 12 A

Explanation:-

According to the Norton theorem, to find the Norton current, first remove the load resistance R_L from the network terminals AB. Short circuit the terminals AB as shown in Figure calculate the current I_Sc or I_N through the short circuit.

Now resistance of 150Ω will not show any effect in the circuit. So only resistance of 30Ω will be effective.

Norton current I_N = 360/30

I_N = 12 A

Answer.1. Synchronous Motor

Explanation:-

Sudden changes of load on synchronous motors may sometimes set up oscillations that are superimposed upon the normal rotation, resulting in periodic variations of a very low frequency in speed. This effect is known as hunting or phase-swinging.

Answer.3. Load Factor

Explanation:-

The ratio of average energy demand to maximum demand during a specific period is called the load factor.

Load Factor = Average Load/Maximum Demand

Answer.1. Capacitance

Explanation:-

Effects and Uses of Capacitors in Electric Circuits

When a capacitor is connected in series in a dc circuit, no current can flow through the capacitor because of the insulating quality of the dielectric. When a voltage is applied to such a circuit, there is a momentary flow of electrons into the negative plate of the capacitor and a corresponding flow out of the positive plate. As soon as the dielectric stress is equal to the applied voltage, the flow of electrons stops. If the voltage is removed, the charge remains in the capacitor until a path is provided through which the electrons can flow from the negative plate hack to the positive plate.

When a capacitor is connected in parallel in a dc circuit, it opposes any change in the circuit voltage. As voltage from the source rises, current flows into the capacitor and thus slows the voltage rise. If the voltage of the source remains at a higher level, the capacitor will charge to that level and will have no further effect on the circuit as long as the voltage remains constant.

As the capacitor charges, its voltage increases, and the amount of charging current decreases. When the capacitor is fully charged to the applied voltage, it completely cancels the battery voltage, thus the current is zero.

The capacitor opposes voltage changes in the circuit. Changing the battery voltage will cause the capacitor to momentarily resist the new voltage, but then it will charge or discharge to the new level. If the battery voltage increased, the capacitor would again try to charge to this higher value. The current would flow momentarily until the capacitor voltage is equal to the battery voltage. If the battery voltage decreased, the capacitor would dis-charge until its voltage equaled the new lower battery voltage. During that discharge time, current flows. This opposition to voltage changes shows up as an opposition to current flow.

If the voltage from the source drops, the capacitor discharges into the circuit and holds the circuit voltage above that of the source for a short time. The property of capacitors to oppose changes in voltage is utilized in dc circuits to reduce or eliminate voltage pulsations.

Answer.3. Condense used steam into water

Explanation:-

• A condenser, as the very name implies, condenses the steam exhausted from the turbine.
• It helps maintain a low pressure (below the atmospheric pressure) at the exhaust. This use of a condenser in a power plant improves efficiency.
• Further, the steam condensed by the condenser may be used as a good source of feed water to the boiler. This results in a reduction of the work on the water treatment plant.
• The efficient operation of the condenser requires a high vacuum to be maintained in the condenser. Any leakage of air into the condenser destroys the vacuum.
• However, the leakage of air cannot be completely eliminated. So, a vacuum pump is absolutely necessary to remove the air leaking into the condenser.

Types of condensers Basically, there are two types of condensers.

(a) mixing type or jet condensers

(b) non-mixing type or surface condensers.

Answer.2. Lagging

Explanation:-

The synchronous machine can operate at lagging, leading, and unity power factors. In the synchronous machine, the total air gap flux is produced by the dc source. If dc excitation is decreased, lagging reactive power will be drawn from the ac source to aid magnetization and thus machine will operate at lagging power factor. If dc excitation is more, leading current drawn from ac source to compensate (oppose) the magnetization and the machine will operate a leading power factor.

Thus it can be concluded that an over-excited motor(Eb  > V) draws a leading current (acts like a capacitive load) but an under-excited motor(E_b < V) draws a lagging current (acts as an inductive load).