Electronic Science - Online Test
Q1. A beam of electrons at rest is accelerated by a potential V. This beam experiences a force F in a uniform magnetic field. The accelerating potential is changed to V’ and the force experienced by the electrons in the same magnetic field is 2F. The ratio V/V’ is
Answer : Option C
Explaination / Solution:
The energy of the electron after being accelerated by a potential V is v is the velocity of the electron.The force it experiences in a magnetic field B is When accelerated by a potential V’, the velocity is and the force in the same magnetic field is
Q2. The number of junctions in a transistor is/are
Answer : Option C
Explaination / Solution:
A transistor consisting of two p-n junctions combined to form either an n-p-n or a p-n-p transistor, having the three electrodes, the emitter, base, and collector
Q3. If 2% of the main current is to be passed through the galvanometer of resistance G, the resistance of shunt required is
Answer : Option C
Explaination / Solution:
The current Ig through a galvanometer of resistance G is 0.02 I where I is the main current.
The shunt resistance S is calculated as follows.
Q4. 
For the NMOSFET in the circuit shown, the threshold voltage is Vth, where Vth > 0. The source voltage VSS is varied from 0 to VDD. Neglecting the channel length modulation, the drain current ID as a function VSS is represented by
Answer : Option A
Explaination / Solution:
We have the following conditions
Since it is in saturation, current ID is given by
Thus, ID - VSS graph shows Parabolic relation for Vss < VDD
- Vth and zero for Vss > VDD
- Vth. Only graph shown in option (A) satisfies this result.
Q5. An 8085 assembly language program is given below.
Line 1: MVI A, B5H
2: MVI B, OEH
3: XRI 69H
4: ADD B
5: ANI 9BH
6: CPI 9FH
7: STA 3010H
8: HLT
The contents of the accumulator just execution of the ADD instruction in line 4 will be
Answer : Option B
Explaination / Solution:
Line 1 : MVI A, B5H ; Move B5H to A
2 : MVI B, 0EH ; Move 0EH to B
3 : XRI 69H ; [A] XOR 69H and store in A
; Contents of A is CDH
4 : ADDB ; Add the contents of A to contents of B and
; store in A, contents of A is EAH
5 : ANI 9BH ; [a] AND 9BH, and store in A,
; Contents of A is 8 AH
6 : CPI 9FH ; Compare 9FH with the contents of A
; Since 8 AH < 9BH, CY = 1
7 : STA 3010 H ; Store the contents of A to location 3010 H
8 : HLT ; Stop
Thus the contents of accumulator after execution of ADD instruction is EAH.
Q6. The electric field between the plates of a fully charged capacitor is E. If a material of dielectric constant k is introduced between the plates, the electric field at a point between the plates
Answer : Option C
Explaination / Solution:
The capacitance C of a capacitor becomes KC when a dielectric is introduced. ;A fully charged capacitor is the capacitor which is charged and then disconnected from the battery. The charge therefore remains constant, The potential reduces to.The electric field therefore becomes
Q7. The switch in the circuit has been closed for a long time. It is opened at t = 0. At t = 0+,
the current through the 1µF capacitor is
Answer : Option B
Explaination / Solution:
No Explaination.
Q8. A closely wound solenoid of 800 turns and area of cross section carries a current of 3.0 A.It is free to turn about the vertical direction and a uniform horizontal magnetic field of 0.25 T is applied.Magnitude of torque on the solenoid when its axis makes an angle of with the direction of applied field
Answer : Option A
Explaination / Solution:
No Explaination.
Q9. Two infinitely long wires carry currents in opposite directions. Then the field at a point P lying midway between them is
Answer : Option C
Explaination / Solution:
When two wires carry currents in the same direction, the magnetic field lines at any point midway between them have the same direction. The magnitudes of the fields add up. If the current in the wires are the same, the field at the midpoint will have twice the magnitude of the field produced by each wire.
Q10. The number of terminals in a transistor is/are
Answer : Option A
Explaination / Solution:
A transistor is an electronic component that can be used as an amplifier, or as a switch. It is made of semiconductor material. Transistors are found in most electronic devices. 
A transistor has three connectors or terminals. In the older bipolar transistor they are the collector, the emitter, and the base. The flow of charge goes in the collector, and out of the emitter, depending on the charge flowing to the base
