Electronic Science - Online Test
Q1. which of the following best describes the difference between electric and magnetic fields
Answer : Option B
Explaination / Solution:
The electrostatic force experienced by a positive charge q placed in an electric field is . The force acts in the direction of the electric field.The magnetic force acting on a charge of magnitude q moving with a velocity 'v' is .This acts in a direction perpendicular to the plane containing the vectors. and
Q2. The instrument for the accurate measurement of the e.m.f of a cell is
Answer : Option D
Explaination / Solution:
Both potentiometer and voltmeter are devices to measure potential difference. E M F is the terminal p.d between the electrodes of a cell in open circuit, i.e., when no current is drawn from it. Potentiometer measures the potential difference using null deflection method, where no current is drawn from the cell; whereas voltmeter needs a small current to show deflection. So, accurate measurement of p.d is done using a potentiometer.
Q3. The voltage gain Av of the circuit shown below is
Answer : Option D
Explaination / Solution:
Q4. When iron filings are sprinkled on a sheet of glass placed over a short bar magnet then,
Answer : Option D
Explaination / Solution:
North pole act as positive end and South pole act as negative end. The iron fillings in the presence of magnetic field gets magnetized and form a tiny magnet which then gets attracted to the poles of bar magnet. North pole of bar magnet attracts south pole of tiny magnet and vice-versa. So all the iron fillings are arranged as the magnetic field lines of bar magnet.
Q5. In the case of semiconductors the valence and conduction bands have
Answer : Option C
Explaination / Solution:
The materials can be classified by the energy gap between their valence band and the conduction band. The valence band is the band consisting of the valence electron, and the conduction band remains empty. Conduction takes place when an electron jumps from valence band to conduction band and the gap between these two bands is forbidden energy gap. Wider the gap between the valence and conduction bands, higher the energy it requires for shifting an electron from valence band to the conduction band.
- In the case of conductors, this energy gap is absent or in other words conduction band, and valence band overlaps each other. Thus, electron requires minimum energy to jump from valence band. The typical examples of conductors are Silver, Copper, and Aluminium.
- In insulators, this gap is vast. Therefore, it requires a significant amount of energy to shift an electron from valence to conduction band. Thus, insulators are poor conductors of electricity. Mica and Ceramic are the well-known examples of insulation material.
- Semiconductors, on the other hand, have an energy gap which is in between that of conductors and insulators. This gap is typically more or less 1 eV, and thus, one electron requires energy more than conductors but less than insulators for shifting valence band to conduction band.
Q6. The DC current gain (β) of a BJT is 50. Assuming that the emitter injection
efficiency is 0.995, the base transport factor is
Answer : Option B
Explaination / Solution:
Q7.
Group I lists four different semiconductor devices. match each device in Group I with its charactecteristic property in Group II
Group-I Group-II
(P) BJT (1) Population iniversion
(Q) MOS capacitor (2) Pinch-off voltage
(R) LASER diode (3) Early effect
(S) JFET (4) Flat-band voltage
Answer : Option C
Explaination / Solution:
In BJT as the B-C reverse bias voltage increases, the B-C space charge region
width increases which xB (i.e. neutral base width) > A change in neutral base
width will change the collector current. A reduction in base width will causes
the gradient in minority carrier concentration to increase, which in turn causes
an increased in the diffusion current. This effect si known as base modulation as
early effect.
In JFET the gate to source voltage that must be applied to achieve pinch off
voltage is described as pinch off voltage and is also called as turn voltage or
threshold voltage.
In LASER population inversion occurs on the condition when concentration of
electrons in one energy state is greater than that in lower energy state, i.e. a non
equilibrium condition.
In MOS capacitor, flat band voltage is the gate voltage that must be applied to
create flat ban condition in which there is no space charge region in semiconductor
under oxide.
Therefore
BJT : Early effect
MOS capacitor : Flat-band voltage
LASER diode : Population inversion
JFET : Pinch-off voltage
Q8. Electric Potential V at a point in an electrical field is
Answer : Option D
Explaination / Solution:
Electric potential V is the work done in bringing unit positive charge from infinity to the point in an electric field, and the potential energy is the work done in bringing any finite charge from infinity to the point in an electric field. They are related as, .If q =1C,
Q9. A lossy capacitor Cx, rated for operation at 5 kV, 50 Hz is represented by an
equivalent circuit with an ideal capacitor Cp in parallel with a resistor Rp. The
value Cp is found to be 0.102 µF and the value of Rp = 1.25 MΩ . Then the power
loss and tan ∂ of the lossy capacitor operating at the rated voltage, respectively,
Answer : Option C
Explaination / Solution:
No Explaination.
Q10. A voltage commutated chopper circuit, operated at 500Hz, is shown below.
If the maximum value of load current is 10A, then the maximum current through the main (M) and auxiliary (A) thyristors will be
Answer : Option A
Explaination / Solution:
