When 100 V dc is applied across a solenoid, a current of 1 A flows in it. When 100 V ac is applied across the same solenoid the current drops to 0.5 A. If the frequency of the ac source is 50 Hz, the impedance and inductance of the solenoid are:
1
200 and 0.55 H
2
100 and 0.86 H
3
200 and 1.0 H
4
100 and 0.93 H
Official Solution
Correct Option: (1)
For the DC case, the impedance is simply the resistance , and the current is given by: For the AC case, the total impedance is the sum of the resistance and the inductive reactance : The impedance for an inductive circuit is given by:
Substitute the values: The inductive reactance is related to the inductance by:
Substitute the frequency :
02
PYQ 2023
medium
physicsID: cuet-ug-
Find the effective impedance in the circuit if the source is:a) DC source and b) High frequency AC source
1
For DC, and for AC,
2
For DC, and for AC,
3
For DC, and for AC,
4
For DC, and for AC,
Official Solution
Correct Option: (2)
For DC, the inductors act as short circuits (because their reactance is zero) and the capacitors act as open circuits (because their reactance is infinite). Therefore, the impedance for a DC source is simply . For high-frequency AC, the inductors act as high-impedance elements, and the capacitors act as low-impedance elements. Therefore, the impedance for a high-frequency AC source is , as the inductors contribute effectively to the impedance while the capacitors' reactance approaches zero.
03
PYQ 2023
medium
physicsID: cuet-ug-
In AC circuits, the relation that holds is , where:
1
in case of a.c. circuit containing R and L in series
2
in case of a.c. circuit containing R and C in series
3
in case of a.c. circuit containing L and C in series
4
in case of a.c. circuit containing R, L, and C in series
Official Solution
Correct Option: (2)
In AC circuits, the impedance is calculated depending on whether the components are resistors, inductors, or capacitors:
- For a circuit containing a resistor and an inductor in series, the impedance is:
- For a circuit containing a resistor and a capacitor in series, the impedance is:
- For a circuit containing only an inductor and a capacitor in series, the impedance is:
Thus, the correct answer is A, B, and C only.
