01) Capacitor is a device used to__________
Answer: store electrical energy
Explanation: Capacitor is used to store the charge. It stores electrical energy between the plates.
02) Capacitor stores which type of energy?
Answer: potential energy
Explanation: Capacitor store charge in between the plates. This charge is stationary so we can say capacitor store potential energy.
03) What is the Power Dissipation formulae?
Answer: direct current
Explanation: Capacitor blocks direct current at steady state and pass alternating current.
04) Why does capacitor block dc signal at steady state?
Answer: Capacitor
Explanation: Frequency of dc signal is zero. So, Capacitive reactance XC=1/2πfc becomes infinite and the capacitor behaves as an open circuit for dc signal. Hence, capacitor block dc signal.
05) Which of the following is a passive device?
Answer: High Current, Low Resistance, Desired (Appreciable) Power
Explanation: Capacitor is a passive device as it consumes power rest all generate power so, they are active devices.
06) What is the value of capacitance of a capacitor which has a voltage of 4V and has 16C of charge?
Answer: 4F
Explanation: Q is directly proportional to V. The constant of proportionality, in this case, is C, that is, the capacitance. Hence Q=CV. From the relation, C=Q/V= 16/4=4F.
07) For which medium capacitance is high?
Answer: Metal
Explanation: Metals are assumed to have a high value of dielectric constant so they have high capacitance.
08) For high frequencies, capacitor acts as _________
Answer: Short circuit
Explanation: Capacitive impedance is inversely proportional to frequency. Hence at very high frequencies, the impedance is almost equal to zero, hence it acts as a short circuit and there is no voltage across it.
09) For very low frequencies, capacitor acts as ________
Answer: Open circuit
Explanation: Capacitive impedance is inversely proportional to frequency. Hence at very low frequencies the impedance is almost infinity and hence acts as an open circuit and no current flows through it.
10) A capacitor consists of_________.
Answer: Two conductors
Explanation: A capacitor consists of two conductors connected in parallel to each other so that it can store charge in between the plates.
11) Capacitance increases with ________.
Answer: Increase in plate area
Explanation: Capacitance is directly proportional to the plate area. Hence as the plate area increases, the capacitance also increases.
12) Capacitance increases with __________.
Answer: Decrease in distance between the plates
Explanation: Capacitance is inversely proportional to the distance between the two parallel plates. Hence, as the distance between the plate decreases, the capacitance increases.
13) Which among the following expressions relate charge, voltage and capacitance of a capacitor?
Answer: Q=CV
Explanation: Q is directly proportional to V. The constant of proportionality in this case is C, that is, the capacitance. Hence Q=CV.
14) If a 2F capacitor has 1C charge, calculate the voltage across its terminals.
Answer: 0.5V
Explanation: Q is directly proportional to V. The constant of proportionality in this case is C, that is, the capacitance. Hence Q=CV. V=Q/C=1/2 V=0.5V.
15) Unit of capacitance is___________.
Answer: Farad
Explanation: Volts is the unit of voltage, Henry for inductance and Newton for a force. Hence the unit for capacitance is Farad.
16) Capacitance is directly proportional to__________
Answer: Area of cross section between the plates
Explanation: The relation between capacitance, area and distance between the plates is: C=epsilon*A/D. According to this relation, the capacitance is directly proportional to the area.
17) The Mark on Ceramic or Non-Polarized Capacitors is “104”. What is the value of Capacitor?.
Answer: 100000 pF
Explanation: Here is the Capacitor marking is “104”
It’s mean that = 10 + 4 Zeros = 1,000,00 pF
= 100 nF = 0.1 µF
18) A capacitor passes AC and blocks DC
Answer: True
Explanation: Capacitive Reactance is given as:
Xc = 1/2 πfC
Where, f is the frequency of applied voltage to the capacitor plates and C is the capacitance.
For DC, the value of f is zero and hence the capacitive reactance is infinite. Since capacitive reactance denotes the opposition to flow of current just like resistance, this implies the capacitor blocks passage of DC current.
Since frequency of AC signals is anything but zero or less than that, capacitive reactance has a finite value for AC supply and allows to pass AC.
19) The formula used to find the capacitance C is __________.
Answer: Q/v
Explanation: Q=cv. Q-charge, V-voltage, c-capacitance.
20) The capacitor doesn’t allow sudden changes in ___________.
Answer: Voltage
Explanation: Any small change in voltage occurs within zero time across the gives an infinite current which is practically impossible. So, in a fixed capacitor, the voltage cannot change abruptly.
21) The Inductor doesn’t allow sudden changes in ___________
Answer: Current
Explanation: Any small change in current occurs within zero time across the gives an infinite voltage which is practically impossible. So, in a fixed inductor, the voltage cannot change abruptly.
22) The units for inductance is _________ and capacitance is ___________
Answer: Henry, Faraday
Explanation: The unit for inductance is ‘Henry’ and capacitance is ‘Faraday’.
23) An Inductor works as a ___________ circuit for DC supply.
Answer: Short
Explanation: Induced voltage across an inductor is zero if the current flowing through it is constant. I.e. Inductor works as a short circuit for DC supply.
24) When the current through an inductor decreases, the amount of energy stored in the electromagnetic field.
Answer: Decreases
25) An inductor, a 1 kΩ resistor, and a switch are connected in series across a 6 V battery. At the instant the switch is closed, the inductor voltage is..
Answer: 6 V
26) The inductance of an iron-core coil decreases if
Answer: The number of turns is decreased
27) Inductance is the property of an inductor that produces an opposition to any change in current. True/false
Answer: True
28) The voltage across a coil when di/dt = 20 mA/μs and L = 8 μH is
Answer: 160 mV
29) Energy is stored by an inductor in an electrostatic field. True/false
Answer: False
30) A 240 μH inductor is equivalent to a
Answer: 0.240 mH inductor
31) Two 10 H inductors are in parallel and the parallel combination is in series with a third 10 H inductor. What is the approximate total reactance when a voltage with a frequency of 7 kHz is applied across the circuit terminals?
Answer: 660 kΩ
32) An inductance of 0.43 mH is smaller than
Answer: 0.05 H
33) Five inductors are connected in series. The lowest value is 8 μH. If the value of each inductor is twice that of the preceding one, and if the inductors are connected in order of ascending values, the total inductance is
Answer: 248 μH
34) When the current through an inductor is cut in half, the amount of energy stored in the electromagnetic field
Answer: Is quartered
35) A sine wave voltage is applied across an inductor. When the frequency of the voltage is decreased, the current
Answer: Is increased
36) An induced voltage is produced as a result of a dc voltage. True/false
Answer: False
37) An inductor and a resistor are in series with a sine wave voltage source. The frequency is set so that the inductive reactance is equal to the resistance. If the frequency is increased, then
Answer: `V_L > V_R`
38) Inductance is indirectly proportional to the square of the number of turns, the permeability, and the cross-sectional area of the core. True/false
Answer: false
39) A switch, a 220 Ω resistor, and a 60 mH inductor are in series across a 20 V battery. What is the current through the inductor two-time constants after the switch is closed?
Answer: 78 mA
40) The term ‘choke’ is more commonly used in connection with an inductor used to block off high frequencies. True/false
Answer: True
41) An inductance of 0.08 μH is larger than
Answer: 0.000000008 H
42) The permeability of a core material is an indication of the ability of the material to establish a magnetic field.
Answer: True
43) An ohmmeter is connected across an inductor and the pointer indicates zero ohms. The inductor is
Answer: Shorted
44) A 2 mH, a 3.3 mH, and a 0.2 mH inductor are connected in series. The total inductance is
Answer: 5.5 mH
45) A 5 mH, a 4.3 mH, and a 0.6 mH inductor are connected in parallel. The total inductance is
Answer: Less than 0.6 mH
46) Inductors add in parallel. True/false
Answer: false
47) Two inductors, `L_1` and `L_2` , are in parallel. `L_1` has a value of 25 μH and `L_2` a value of 50 μH. The parallel combination is in series with `L_3`, a 20 μH coil. The entire combination is across an ac source of 60 `V_rms` at 300 kHz. The total RMS current is
Answer: 870 mA
48) The winding resistance of a coil can be increased by
Answer: Increasing the number of turns or using thinner wire
49) All coil cores are made of iron. True/false
Answer: False
50) The current through a 120 mH coil is changing at a rate of 150 mA/s. The voltage induced across the coil is
Answer: 18 mV
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