Electronic Science - Online Test
Q1. Submarine cables act as
Answer : Option B
Explaination / Solution:
A submarine cable consists of an inner conductor which carries power. This conductor is covered by an insulator, which acts as a dielectric. The dielectric material is covered by a metal coating called shield, which is connected to ground.
The cable acts as a cylindrical capacitor, with the conductor acting as the inner cylinder, and the metal shield as the outer cylinder which is connected to earth.
The cable acts as a cylindrical capacitor, with the conductor acting as the inner cylinder, and the metal shield as the outer cylinder which is connected to earth.
Q2. Two passive two-port networks are connected in cascade as shown in figure. A voltage source is
connected at port 1.
Given V1 = A1V2 + B1I2
I1 = C1V2 + D1I2
V2 = A2V3 + B2I3
A1 ,B1 ,C1 ,D1 ,A2 ,B2 ,C2 and D2 are the generalized circuit constants. If the Thevenin equivalent
circuit at port 3 consists of a voltage source VT and impedance ZT connected in series, then
Answer : Option D
Explaination / Solution:
Q3. A potentiometer wire, 10 m long, has resistance 40 ohms. It is put in series with a resistance 760 ohms and connected to a 2 volt battery. The potential gradient in the wire is :
Answer : Option A
Explaination / Solution:
The total resistance is the sum of the resistance of the potentiometer and the external resistance.
Current through the potentiometer is
The potential drop across the potentiometer
The potential gradient = ( potential drop across the potentiometer)/ length of the potentiometer wire)
Q4. A cylinder of iron is placed so that it is free to rotate around its axis. Initially the cylinder is at rest, and a magnetic field is applied to the cylinder so that it is magnetized in a direction parallel to its axis. If the direction of the external field is suddenly reversed, the direction of magnetization will also reverse and the cylinder will begin rotating around its axis because
Answer : Option D
Explaination / Solution:
No Explaination.
Q5. A bar magnet is equivalent to
Answer : Option A
Explaination / Solution:
A solenoid carrying current produces a magnetic field very similar to that of bar magnet. The magnetic field lines emerge from the ends of a solenoid and the number of field lines near its perpendicular bisector is almost equal to zero. A circular coil produces field along its axis. A straight conductor produces a magnetic field that can be represented by concentric circles. A toroid is a solenoid that has collapsed on itself. The field in a toroid is confined to the ring like region bounded by the toroid.
Q6. To provide the abundance of holes the impurity added should be
Answer : Option C
Explaination / Solution:
If We introduce a "Trivalent" (3-electron) impurity into the crystalline structure, such as Aluminium, Boron or Indium, which have only three valence electrons available in their outermost orbital, the fourth closed bond cannot be formed. Therefore, a complete connection is not possible, giving the semiconductor material an abundance of positively charged carriers known as "holes" in the structure of the crystal where electrons are effectively missing
Q7. For the circuit shown, the counter state (Q1Q0) follows the sequence
Answer : Option A
Explaination / Solution:
Q8. In the circuit below, the diode is ideal. The voltage V is given by
Answer : Option A
Explaination / Solution:
Let diode be OFF. In this case 1 A current will flow in resistor and voltage across resistor will be V = 1.V
Diode is off, it must be in reverse biased, therefore
Vi- 1 > 0 " Vi > 1
Thus for Vi > 1 diode is off and V = 1V
Option (B) and (C) doesn’t satisfy this condition.
Let Vi < 1. In this case diode will be on and voltage across diode will be zero and
V = Vi
Thus V = min(Vi,1)
Q9. Dielectric polarization is the phenomenon
Answer : Option C
Explaination / Solution:
Atomic dipoles in a dielectric experience a torque when placed in an external electric field. As a result of this torque, they align themselves in the direction of the electric field, since thi is the position of least potential energy. This phenomenon in which the atomic dipoles align themselves in the diorection of the electric field is called dielectric polarization.
Q10. The switch in the figure below was closed for a long time. It is opened at t = 0. The current in
the inductor of 2 H for
t ≥ 0 is
Answer : Option A
Explaination / Solution:
