Electronic Science - Online Test
Q1. The conductivity of P – type semiconductor is due to
Answer : Option A
Explaination / Solution:
No Explaination.
Q2.
Compared to a p-n junction with NA = ND = 10-14/cm3, which one of the following statements is TRUE for a p-n junction with NA = ND = 10-20/cm3?
Answer : Option C
Explaination / Solution:
Reverse bias breakdown or Zener effect occurs in highly doped PN junction through tunneling mechanism. In a highly doped PN junction, the conduction and valence bands on opposite sides of the junction are sufficiently close during reverse bias that electron may tunnel directly from the valence band on the p-side into the conduction band on n-side.
Breakdown voltage 
So, breakdown voltage decreases as concentration increases
Depletion capacitance
Depletion capacitance increases as concentration increases
Q3. The following Karnaugh map represent a function F.
Which of the following circuits is a realization of the above function F?
Answer : Option D
Explaination / Solution:
No Explaination.
Q4. Transformer and emitter follower can both be used for impedance matching at the output of an audio amplifier. The basic relationship between the input power Pin and output power Pout in both the cases is
Answer : Option A
Explaination / Solution:
No Explaination.
Q5. A series RL circuit is excited at t = 0 by closing a switch as shown in the figure.
Assuming zero initial conditions, the value of 
is
is
Answer : Option D
Explaination / Solution:
Q6. A variable capacitor and an electroscope are connected in parallel to a battery. The reading of the electroscope would be decreased by
Answer : Option C
Explaination / Solution:
An electroscope is a device which measures the potential difference. If it is connected in parallel to the capacitor, the potential across it will be equal to the potential across the capacitor, which is equal to the potential across the battery. On decreasing the battery potential, the potential difference across the electroscope reduces and hence the reading reduces. While the capacitor is connected to the battery, Placing a dielectric between the plates, or decreasing the distance between the plates or increasing the area of the plates will not change the potential difference across it; since it will always remain equal to the potential difference maintained by the battery. In the cases B, C and D, The capacitance of the capacitor , however increases ; but this increase happens due to increase in the charge stored in the capacitor while the potential remains constant.
Q7. In the ac equivalent circuit shown in the figure, if iin is the input current and Rf is very larger, the type of feedback is
Answer : Option B
Explaination / Solution:
From the circuit, we observe that output is Vout (Voltage). Feedback is current
through resistance Rf , which is added to input current iin . Thus, the configuration
is voltage-current feedback.
Q8. A milliammeter of range 10 mA and resistance 9 ohms is joined in a circuit as shown. The device gives full-scale deflection for current I when A and B are used as its terminals, i.e., current enters at A and leaves at B (C is left isolated). The value of total current I is
Answer : Option D
Explaination / Solution:
Thee above circuit can be redrawn as:
Total resistance in the arm EF ( milliammeter and the 0.9Ω resistor)= 9+0.9=9.9Ω.
Since the milliammeter gives full scale deflection when A and B are used as its terminals, the current in the arm EF is 10 mA. The potential difference across the arm is
VEF = Ig* R = 10(10^ - 3) * 9.9 = 0.099V.
The potential difference across AB= potential diff across the 0.1Ω resistor= VEF = 0.099 V.
The current through the 0.1Ω resistor
The total current I is the sum of I0.1 and Ig
= Ig + I0.1 = 0.01 + 0.99 = 1A.
Q9. The magnetic field due to a current carrying circular loop of radius 3 cm at a point on the axis at a distance of 4 cm from the centre is 54 μT. what will be its value at the centre of the loop?
Answer : Option D
Explaination / Solution:
The magnetic field at the centre of a coil of radius R and number of turns N , carrying a current I is . At a point distance x from the coil, the field is
Q10. A cube-shaped permanent magnet is made of a ferromagnetic material with a magnetization M of about The side length is 2 cm. Magnetic dipole moment of the magnet is.
Answer : Option B
Explaination / Solution:
No Explaination.
