Electronic Science - Online Test
Q1. A cube-shaped permanent magnet is made of a feromagnetic matrerial with a magnetization M of about The side length is 2 cm. Magnetic field due to the magnet at a point 10 cm from the magnet along its axis is
Answer : Option B
Explaination / Solution:
No Explaination.
Q2.
A P– type crystal is obtained by doping
A) silicon with arsenic,
B) silicon with aluminum,
C) Ge with boron,
D) Ge with phosphorus.
Answer : Option A
Explaination / Solution:
Doping means the introduction of impurities into a semiconductor crystal to the defined modification of conductivity.
In P-Type Semiconductor, The addition of trivalent impurities such as boron, aluminum or gallium to an intrinsic semiconductor creates deficiencies of valence electrons,called "holes".
Q3. 
Consider the common emitter amplifier shown below with the following circuit parameters:
The lower cut-off frequency due to C2 is
Answer : Option B
Explaination / Solution:
Cut-off frequency due to C2
Lower cut-off frequency
Q4. The complete set of only those Logic Gates designated as Universal Gates is
Answer : Option C
Explaination / Solution:
No Explaination.
Q5. In a p n junction diode under reverse biased the magnitude of electric field is maximum at
Answer : Option C
Explaination / Solution:
The electric field has the maximum value at the junction of p n.
Q6. A three-winding transformer is connected to an AC voltage source as shown in the figure.
The number of turns are as follows: N1 = 100, N2 = 50. If the magnetizing current is
neglected, and the currents in two windings are 
and 
then
what is the value of the current 
in Ampere?
and then
what is the value of the current in Ampere?
Answer : Option A
Explaination / Solution:
Q7. To make a condenser of 16 μF, 1000 volts, how many condensers are needed which have written on them “8 μF, 250 volts”?
Answer : Option D
Explaination / Solution:
Each capacitor of capacitance can withstand a maximum potential of 250 V. When equal capacitors are connected in series, the potential difference across them is equal. If there are m capacitors in series such that the potential across each is 250 V, then,. The equivalent capacitance of 4 capacitors connected in series is.To achieve a capacitance of 16 , n such rows of capacitors need to be connected in parallel. .To make a condenser of 16,8 rows of capacitors with each row containing 4 capacitors are to be connected. The total number of capacitors= n×m=4×8=32.
Q8. 
In the circuit shown below what is the output voltage (vout)if a silicon transistor Q and an ideal op-amp are used?
Answer : Option B
Explaination / Solution:
For the given ideal op-amp, negative terminal will be also ground (at zero voltage) and so, the collector terminal of the BJT will be at zero voltage.
i.e., VC = 0 volt
The current in 1 kΩ resistor is given by
This current will flow completely through the BJT since, no current will flow into the ideal op-amp (I/P resistance of ideal op-amp is infinity). So, for BJT we have
i.e.,the base collector junction is reverse biased (zero voltage) therefore, the collector current (IC ) can have a value only if base-emitter is forward biased.
Hence,
Q9. Mobility is defined as
Answer : Option D
Explaination / Solution:
Mobility is defined as the drift velocity acquired by the charge per unit electric field strength. Faster the particle moves in a given electric field strength greater is the mobility.
Q10. A long wire carries a steady current. It is bent into a circle of one turn and the magnetic field at the centre of the coil is B. It is then bent into a circular loop of n turns. The magnetic field at the centre of the coil will be
Answer : Option C
Explaination / Solution:
If the length of the wire is L and the radii of the coils in two cases be and . Then,
