EE MCQ

SSC JE Electrical 2019 with solution SET-2
######
Which of the following motors can be connected across a single-phase AC supply?

A DC motor can be operated from a single-phase AC supply.

The direction of the torque produced by a DC machine is determined by the direction of current flow in the armature conductors and by the polarity of the field.

Torque is developed in a DC machine because the commutator arrangement permits the field and armature currents to remain in phase, thus producing torque in a constant direction.

A similar result can be obtained by using an AC supply, and by connecting the armature and field windings in series.

Related Question

SSC JE Electrical 2019 with solution SET-2
######
In the two-wattmeter method of three-phase power measurement of a balanced load, if the reading of one meter is −200W, then the power factor of the load is

The reading of two wattmeters can be expressed as

W1 = VLILcos(30 + φ)

W2 = VLILcos(30 − φ)

(i) When PF is unity ( φ = 0°)

W1 = VLILcos30°

W2 = VLILcos30°

Both wattmeters read equal and positive reading i.e upscale reading

(ii) When PF is 0.5 (φ = 60°)

W1 = VLILcos90° = 0

W2 = VLILcos30°

Hence total power is measured by wattmeter W2 alone

(iii) When PF is less than 0.5 but greater than 0 i.e ( 90° > φ > 60°)

W1 = Negative

W2 = positive (since cos(−φ) = cosφ)

The wattmeter W2 reads positive (i.e.upscale) because for the given conditions (i.e. ( 90° > φ > 60°), the phase angle between voltage and current will be less than 90°. However, in wattmeter W1, the phase angle between voltage and current shall be more than 90° and hence the wattmeter gives negative (i.e. downscale) reading.

SSC JE Electrical 2019 with solution SET-2
######
Four relations have been given. Select the correct relation?

The amount of flux produced by the magnet indicates the strength of the magnet. The more the magnetizing force (MMF), the more is the flux produced. The more the opposition to the flux path (i.e., reluctance or magnetic resistance) less is the flux produced. This relationship is expressed as

Flux = MMF/ Reluctance

Reluctance is the opposition offered by the material in the flux path to the establishment of the flux. The reluctance in a magnetic circuit is similar to the resistance in an electric circuit. Reluctance is the inverse of permeance.

MMF = Flux/Permeance

SSC JE Electrical 2019 with solution SET-2
######
Four options have been given, out of which three are alike in some manner and one is different. Select the odd one?

⇒ The electric potential at a point is defined as the work done in bringing the unit positive charge ( +1C) from infinity to that point. The work done is independent of the path taken. Its unit is **Volt (V)**.

⇒ Potential Difference (pd or V) is a measure of the difference in charge between two points in a conductor. Its unit is **Volt (V)**.

⇒ The difference in charge produced by the battery is stored in the battery as electrical potential energy and is called electromotive force (shortened to emf). Electromotive force is also measured in volts. Its unit is **Volt (V)**.

⇒ Electric flux is a measure of how much the electric field vectors penetrate through a given surface. The SI unit of electric flux is **N.m2/C**.

Electrical potential, Potential difference, Electromotive force has the same SI unit i.e Volt (V). Hence Electric flux is alike from others.

SSC JE Electrical 2019 with solution SET-2
######
Observe the figure and find the correct relation from the four given options?

According to Kirchhoff’s law states that the current entering a node is always equal to the current leaving a node.

From the above Diagram

Current Flowing towards the Point: I1, I2, I6

Current Flowing Away from the Point: I3, I4, I5

Hence I1 + I2 + I6 = I3 + I4+ I5

SSC JE Electrical 2019 with solution SET-2
######
A diode appears as in forward region of its characteristics?

A P-N junction acts as a voltage-controlled switch. During forward biasied the p-n junction diode acts like an ON switch. When reverse biased, it acts like an OFF switch.