The dielectric strength of air is 3.0×1026 V/m. A parallel-plate air-capacitor has area 20 cm2 and plate separation 0.10 mm. Find the maximum rms voltage of an AC source which can be safely connected to this capacitor.
How does an inductor behave in DC?
- 60 s
- 1120 s
- 160 s
- 1240 s
1) Find the impedance of the circuit.
2) Find the time lag between max. alternating voltage and current.
- 4π2 mA
- 30 mA
- 6 mA
- 200 mA
The plates are very large and close together (area = A, separation = d).
Neglecting the edge effects, find the displacementcurrent through the capacitor?
q= electric charge, R= electric resistance,
C= electric capacitance. The dimensional formula for is
Which is more Powerful AC or DC?
E=30θ−θ215. The neutral temperature for the thermo-couple will be
Four resistors of , , and are connected in series to a battery. Calculate the current in resistor.
i) Under which conditions would the rms currents in the two circuits be the same?
ii) Can the rms current in circuit (b) be larger than
that in (a)?
A cell of is connected to an external resistance of , when. recorded at the ends of resistance is . Calculate the internal resistance of the cell.
- 10 μ C
- 90 μ C
- 100 μ C
- None of these
- 20 V
- 10 V
- 5 V
- 25 V
Which is not true for three-phase AC?
The three-phase power supply has three distinct wave cycles.
The voltage of three-phase is 230 V.
The efficiency of three-phase is high compared to single-phase
Three-phase is expensive compared to single-phase
The phase difference between the input and output voltage of CE amplifier circuit is
(i). M=2.5×10−9 H
(ii). e=2.5×10−9 V
(iii). M=5×10−9 H
(iv). e=5×10−9 V
- (i) and (ii)
- (ii) and (iii)
- (i) and (iv)
- (ii) and (iv)
- Low resistance in parallel
- Low resistance in series
- High resistance in parallel
- High resistance in series
Answer the following questions:
(a) In any ac circuit, is the applied instantaneous voltage equal to the algebraic sum of the instantaneous voltages across the series elements of the circuit? Is the same true for rms voltage?
(b) A capacitor is used in the primary circuit of an induction coil.
(c) An applied voltage signal consists of a superposition of a dc voltage and an ac voltage of high frequency. The circuit consists of an inductor and a capacitor in series. Show that the dc signal will appear across C and the ac signal across L.
(d) A choke coil in series with a lamp is connected to a dc line. The lamp is seen to shine brightly. Insertion of an iron core in the choke causes no change in the lamp’s brightness. Predict the corresponding observations if the connection is to an ac line.
(e) Why is choke coil needed in the use of fluorescent tubes with ac mains? Why can we not use an ordinary resistor instead of the choke coil?
The phase difference between input and output voltages of a CE circuit is