EE MCQ

SSC JE Electrical 2019 with solution SET-1
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An electric heater is connected across 230V and it draws a current of 2A. Then the resistance offered by the heater is?

Given

Voltage V = 230 V

Current I = 2 A

Resistance R = V/I

R = 230/2 = 115 Ω

Related Question

SSC JE Electrical 2019 with solution SET-1
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The output of the logic circuit given below represents the gate.

In the given diagram all are NOR Gate . The final output is shown in the figure.

At stage 1 the output will be \overline A \& \overline B

At stage 2 the output will be \overline {\overline A + \overline B } = A.B

And the final output will be \overline {A.B}

Hence for input A & B the output is \overline {AB} in case of Nand gate.

SSC JE Electrical 2019 with solution SET-1
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________ is used to manufacture stay wire, earth wire, and structural components

Galvanized steel conductors do not corrode, and possess high resistance. Hence such Wires are used in telecommunications circuits, earth wires, guard wire, stray wire, etc.

SSC JE Electrical 2019 with solution SET-1
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Z1 and Z2 are connected in series to form a load. A wattmeter’s current coil is connected in series with the load, whereas its pressure coil is connected across Z2. The wattmeter reads

As you can see from the below figure in load Z1 is connected with the only current coil. In Load Z2 both current from the current coil (CC) and voltage from voltage coil (PC) are present (Power = V × I). Hence the Wattmeter will read power consumed by Z2.

SSC JE Electrical 2019 with solution SET-1
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The ratio of conductor voltage and the voltage across the disc nearest to the conductor multiplied by the number discs are

The non -uniformity in the voltage distribution over a string of suspension insulators is expressed in terms of a parameter called “string efficiency“.

The voltage across the unit nearer to the conductor is more than the voltage in the unit nearer to the support. This unequal potential distribution over the string is expressed in terms of string efficiency.

The efficiency of a string is defined as the ratio of voltage across the whole string to the product of the number of discs and the voltage across the disc nearest to the line conductor. Mathematically, it can be expressed as,

Where n = Number of the unit in the string

The more the value of the string efficiency, the more uniform is the voltage distribution across the string. For the ideal case, the string efficiency is 100% and the voltage across each disc of the string is equal. Practically various methods are used to obtain string efficiency as high as possible.

SSC JE Electrical 2019 with solution SET-1
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A three-phase induction machine, when it is operating like a motor, the range of slip is given by

Torque speed characteristic of induction motor

Motoring mode: 0 ≤ s ≤ 1

For this range of slip, the load resistance in the circuit is positive, i.e. torque developed is in the direction in which the rotor rotates.

In this region the value of slip lies between 0 to 11 i.e., slip is positive.

The motor rotates in the same direction as that of a rotating magnetic field.

At s = 0 (synchronous speed), the torque produced by the motor is zero because the induced voltage in the rotor is zero when N= Ns.

The torque increases as the slip increases while the air gap flux remains constant.

The torque-slip characteristic from no-load to somewhat beyond full-load is almost linear.

Generating mode: s <0

In this operating mode, the slip s is negative i.e., s < 0. The slip will be negative if and only if the rotor speed N is greater than the synchronous speed Ns (N> Ns). However, the rotor and R.M.F both rotate in the same direction.

In this region, the motor acts as a generator and return the power back to a.c. source.

Braking or plugging Mode: s > 1

In this region, the value of slip is greater than 1 and the rotor rotates in the opposite direction of the rotating magnetic field.

This is achieved by interchanging any two phases of the stator supply.