Electronic Science - Online Test

UGC NET Entrance exams Science Electronic Science TEST : 45

UGC NET Entrance exams Science # Electronic Science Current Electricity Prepare / Learn

Q1. In a Wheatstone’s bridge, P = 9 ohms, Q = 11 ohms, R = 4 ohms and S = 6 ohms. How much resistance must be put in parallel to the resistance S to balance the wheatstone bridge?

A. 26.4 ohms

B. (44/9) ohms

C. 18.7 ohms

D. 24 ohms

Answer : Option A
Explaination / Solution:

Let a resistance M be put in parallel to S and the equivalent resistance of the parallel combination be X. In the bridge balance condition

$\begin{array}{l} \frac{X}{R} = \frac{Q}{P} \\ \Rightarrow X = R \times (\frac{Q}{P}) \\ X = 4 \times \frac{11}{9} = \frac{44}{9} \end{array}$

In the parallel combination of S and M,

$\begin{array}{l} \begin{array}{l} \frac{1}{X} = \frac{1}{S} + \frac{1}{M} \\ \frac{1}{M} = \frac{1}{X} - \frac{1}{S} \\ \Rightarrow \frac{1}{M} = \frac{9}{44} - \frac{1}{6} = \frac{10}{264} \end{array} \\ ∴ M = 26.4 Ω \end{array}$

UGC NET Entrance exams Science # Electronic Science Magnetism and Matter Prepare / Learn

Q2. A short bar magnet placed with its axis at

30

with a uniform external magnetic field of 0.25 T experiences a torque of magnitude equal to

4.5 \times 1 0^{- 2}

J. What is the magnitude of magnetic moment of the magnet?

A. 0.30 J/T

B. 0.36 J/T

C. 0.33 J/T

D. 0.26 J/T

Answer : Option B
Explaination / Solution:
No Explaination.

UGC NET Entrance exams Science # Electronic Science Moving Charges and Magnetism Prepare / Learn

Q3. Two straight horizontal parallel wires are carrying the same current in the same direction, d is the distance between the wires. You are provided with a small freely suspended magnetic needle. At which of the following positions will the orientation of the needle be independent of the magnitude of the current in the wires

A. at a distance d/2 from any of the wires in the horizontal plane

B. at a distance d/2 from any of the wires

C. anywhere on the circumference of a vertical circle of a radius d and centre

D. at points halfway between the wires in the horizontal plane.

Answer : Option D
Explaination / Solution:

Consider two wires carrying current in the same direction as shown. The current acts inwards to the plane of the screen. The magnetic field lines are in the plane of the screen and are concentric circles. At the point midway between the wires, the field lines are directed opposite to each other. The magnetic fields due to

the two wires are directed opposite to each other. They also have the same magnitude since the wires carry currents of equal magnitude. At a distance d/2, in the horizontal plane, the net magnetic field is zero. A magnetic needle placed at this point experiences no force. The orientation of the needle becomes independent of the current in the wires

UGC NET Entrance exams Science # Electronic Science Electronic Devices Prepare / Learn

Q4. For forward biasing a P-N junction the positive terminal of the battery is connected to

A. N – type crystal

B. Neither P – type nor N – type crystal

C. P – type crystal

D. Either P –type or N – type crystal

Answer : Option C
Explaination / Solution:

Biasing is the application of a voltage across a p–n junction.

When we connect p-type region of a junction with the positive terminal of a voltage source and n-type region with the negative terminal of the voltage source, then the junction is said to be forward biased.

At this condition, due to the attraction of positive terminal of source, electrons which participated in covalent bond creations in p-type material, will be attracted towards the terminal.

UGC NET Entrance exams Science # Electronic Science Digital Circuits Prepare / Learn

Q5. An 8255 chip is interfaced to an 8085 microprocessor system as an I/O mapped I/O as show in the figure. The address lines A₀ and A₁ of the 8085 are used by the 8255 chip to decode internally its thee ports and the Control register. The address lines A₃ to A as well as the

signal are used for address decoding. The range of addresses for which the 8255 chip would get selected is

A. F8H - FBH

B. F8GH - FCH

C. F8H - FFH

D. F0H - F7H

Answer : Option C
Explaination / Solution:

UGC NET Entrance exams Science # Electronic Science Current Electricity Prepare / Learn

Q6. In the measurement of resistance by a metre bridge, the current is necessarily reversed through the bridge wire to eliminate

A. Index errors

B. Random errors

C. Error due to thermoelectric effects

D. End errors

Answer : Option D
Explaination / Solution:

The connecting metal strips include a small resistance in the circuit called the end resistance. On reversing the current, the end resistance tends to get cancelled out.

UGC NET Entrance exams Science # Electronic Science Electronic Devices Prepare / Learn

Q7.

Consider the following two statements about the internal conditions in a n - channel MOSFET operating in the active region.

S1 : The inversion charge decreases from source to drain

S2 : The channel potential increases from source to drain.

Which of the following is correct?

A. Only S2 is true

B. Both S1 and S2 are false

C. Both S1 and S2 are true, but S2 is not a reason for S1

D. Both S1 and S2 are true, and S2 is a reason for S1

Answer : Option D
Explaination / Solution:

Both S1 and S2 are true and S2 is a reason for S1.

UGC NET Entrance exams Science # Electronic Science Electrostatic Potential and Capacitance Prepare / Learn

Q8. When a capacitor is connected to a battery

A. an alternating current flows in the circuit.

B. a current flows in the circuit for sometime and then decreases to zero

C. no current flows in the circuit at all

D. the current keeps on increasing, reaching a maximum value when the

Answer : Option B
Explaination / Solution:

When an uncharged capacitor is connected to a battery, charges flow from the poles of the battery to the plates of the capacitor and this process continues till the potential across the capacitor attains the potential difference of the battery. The current flows in the circuit till the time the capacitor is charged and then it ceases.

UGC NET Entrance exams Science # Electronic Science Electric Circuits Prepare / Learn

Q9. A load is supplied by a 230 V, 50 Hz source. The active power P and the reactive power Q consumed by the load are such that 1 kW ≤ P ≤ 2kW and 1kVAR ≤ Q ≤ kVAR . A capacitor connected across the load for power factor correction generates 1 kVAR reactive power. The worst case power factor after power factor correction is

A. 0.447 lag

B. 0.707 lag

C. 0.894 lag

D. 1

Answer : Option B
Explaination / Solution:

UGC NET Entrance exams Science # Electronic Science Magnetism and Matter Prepare / Learn

Q10.

A closely wound solenoid of 800 turns and area of cross section

2.5 \times 1 0^{- 4} m^{2}

carries a current of 3.0 A. What is its associated magneticm oment?

A. 0.8 J/T

B. 0.5 J/T

C. 0.4 J/T

D. 0.6 J/T

Answer : Option D
Explaination / Solution:
No Explaination.

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UGC NET Entrance exams Science Electronic Science TEST : 45