Electronic Science - Online Test
Q1. A piece of copper and another of germanium are cooled from room temperature to 80K. The resistance
Answer : Option B
Explaination / Solution:
Copper is a conductor and we know that for conductors, resistance is directly proprtional to temperature. Therefore on decreasing temperature resistance also decreases.
Whereas, germanium is a semiconductor and for semiconductors, resistance is inversely proportional to temperature. So on decreasing temperature resistance increases.
Q2. A parallel combination of 0.1 MΩ resistor and a 10 μF capacitor is connected across a 1.5 V source of negligible resistance. The time (in seconds) required for the capacitor to get charged up to 0.75 V is approximately
Answer : Option A
Explaination / Solution:
A capacitor is charged when the resistance is connected in series with the capacitor. The time constant of the circuit . The capacitor will not be charged.
Q3.
For small increase in VG beyond 1V, which of the following gives the correct description of the region of operation of each MOSFET
Answer : Option D
Explaination / Solution:
For small increase in VG beyond 1 V the n - channel MOSFET goes into saturation as VGS + ive and p - MOSFET is always in active region or triode region.
Q4. For the circuit shown in the following, I0 - I3 are inputs to the 4:1 multiplexers,
R(MSB) and S are control bits. 
The output Z can be represented by
Answer : Option A
Explaination / Solution:
Q5. A closely wound solenoid of 2000 turns and area of cross-section , carrying a current of 4.0 A, is suspended through its centre allowing it to turn in a horizontal plane. If a uniform horizontal magnetic field of T is set up at an angle of with the axis of the solenoid,force and torque on the solenoid are
Answer : Option A
Explaination / Solution:
No Explaination.
Q6. A steel wire of length l has a magnetic moment M. It is then bent into a semicircular arc. The new magnetic moment is
Answer : Option D
Explaination / Solution:
If the steel wire is assumed to be a bar magnet of length l and pole strength qm, its magnetic momentWhen it is bent into a semicircular arc of radius r, the distance between the poles is equal to its diameter The new magnetic moment .Since,
Q7. To use a transistor as an amplifier
Answer : Option C
Explaination / Solution:
Amplifier is an electronic device. The device which increases the value of a signal is called amplifier. In input a weak signal is applied, in output a strong, same shape signal is gained. Amplify means to increase the value of something.
The collector is reverse biased and the emitter is forward biased while using transistor as an amplifier.
Q8. The L-C circuit shown in the figure has an inductance L = 1mH and a capacitance C = 10µF. 
The L – C circuit of Q.9 is used to commutate a thyristor. Which is initially carrying a current of 5 A as shown in the figure below. The values and initial conditions of L and C are the same as in Q.9. The switch is closed at t=0. If the forward drop is negligible, the time taken for the device to turn off is
Answer : Option A
Explaination / Solution:
No Explaination.
Q9. The equivalent resistance of two resistances P and Q which are in series is
Answer : Option C
Explaination / Solution:
Equivalent resistance of two resistances connected in series is equal to the sum of the two resistances.
Q10.
Consider the situation shown in the figure. The capacitor A has a charge q on it whereas B is uncharged. The charge appearing on the capacitor B a long time after the switch is closed is
Answer : Option D
Explaination / Solution:
the charge –q is bound to the charge +q. Therefore no charge will appear on the capacitor B. The capacitor B will acquire a charge only if a battery ( driving force) is put in the circuit.
