Ques 31. A 10 μF and a 20μF capacitor are in series. The combination is supplied at 150 V from a sinusoidal voltage source. The voltage across the 20μF capacitor is then
75 V
125 V
100 V
50 V✔
The potential difference across capacitor is inversely proportional to its capacitance in series combination
V ∝ 1/C
Voltage across 20 μf capacitor is
V20μf = 150 x C1/(C1 + C2)
= 1500/(10+20)
= 50 V
Ques 32. The conditions at which the following potential divider is independent of frequency may be
R1/R2 = C1/C2
R1/R2 = C2/C1✔
R1C1 << 1, R2C2 <<1
R1 + R2 + 1/C1 + 1/C2
ii and iv are true
1 and iii are true
i is true only
ii is true only
For independent frequency time constants, RC network must be equal i.e the circuit has an output which is independent of frequency if the low and high-frequency response is identical.
Vo = R1/(R1 + R2) = C2/(C1 + C2)
= R1C1 = R2C2
R1/R2 = C2/C1
Ques 33. Which of the following is the best conductor of electricity?
Warm water
Salt Water✔
Cold Water
Distilled water
The conductivity of water depends on the concentration of dissolved ions in the solution. Salt molecules are made of sodium ions and chloride ions. (An ion is an atom that has an electrical charge because it has either gained or lost an electron.) When we put salt in water, the water molecules pull the sodium and chlorine ions apart so they are floating freely which is responsible for the conductance of electricity.
So, pure/distilled water is an extremely bad conductor, while impure water with ions in it is a good conductor
Ques 34. The wave shape of current flowing through an inductor is
The wave shape of voltage drop (v) across the inductor is
Answer a
i = 2.t/T
Voltage across an inductor at any moment in time t is V = Ldi/dt
Ques 35. SI unit of electrical energy is
Watt-second
Joule✔
KWh
Volt-ampere-Second
The electrical energy consumed in a circuit is defined as the total work done in maintaining the current in an electrical circuit for a given time.
S.I. unit of electrical energy is Joule whereas the commercial unit of electrical energy is a kilowatt-hour (kWh).
Ques 36. Two wires A and B of the same material but of different lengths L and 2L have the radius r and 2r respectively. The ratio of specific resistance will be
1:4
1:8
1:1✔
1:2
Specific resistance defines as resistance offered by the material per unit length and unit area. Therefore, it is independent of the length and area of the material. Hence, for the same material, the specific resistance of the wire with any length and area always be the same. Hence, the ratio always is unity.
Ques 37. A 20 microfarad capacitor is connected across an ideal voltage source. The current in the capacitor
Will be very high at first, then exponentially decay
Will be very high at first, then exponentially decay and at steady state will become zero✔
Will be zero at first, then exponentially rise
None of these is true
The voltage across a capacitor cannot change instantaneously as some time is required for the electric charge to build upon or leave the capacitor plates. As the capacitor begins to charge the circuit current rises very rapidly.
Now the capacitor is charged, the rate of change of voltage slows, and the charge slows as the charging current falls. The curve describing the charging of the capacitor follows a recognizable mathematical law describing an exponential curve until the current is practically zero and the voltage across the capacitor is at its maximum.
Ques 38. In general, if a sine wave is fed into a Schmitt trigger, the output will be
A square wave✔
A sawtooth wave
An amplified sine wave
A triangular wave
A Schmitt trigger is a device (or the input portion of a device) that has separate thresholds for a rising signal and a falling signal. It is a positive feedback circuit that holds the output level till the input signal to the comparator is higher than the threshold.
The positive feedback is introduced by adding a part of the output voltage to the input voltage.
Ques 39. To the given circuit the function of the diode D is
To protect the base-emitter junction✔
To hold the output voltage to a constant value
To bias the transistor
To clip the output voltage
The absolute max voltage rating for the base-emitter voltage is the lowest of all values. This low value means the B-E junction must be protected from a high reverse voltage. A diode is used for an NPN transistor. In this manner, the logging transistor’s base-emitter junction is prevented from being reverse-biased.
Ques 40. FETs are
Either unipolar or Bipolar
Unipolar device✔
Bipolar Device
None of these
FETs are also known as unipolar transistors since they involve single-carrier-type operation.
