An ac circuit resonates at a frequency of 10 kHz. If its frequency is ...
To understand why the impedance of an AC circuit increases and becomes inductive when the frequency is increased, we need to consider the behavior of inductors and capacitors at different frequencies.
1. Behavior of Inductors:
- An inductor is a device that stores energy in its magnetic field.
- At low frequencies, the reactance of an inductor (Xl) is small, and its impedance (Z) is primarily determined by its resistance (R).
- As the frequency increases, the reactance of the inductor also increases. The reactance of an inductor is given by the formula Xl = 2πfL, where f is the frequency and L is the inductance.
- When the frequency reaches a certain point, called the resonant frequency, the reactance of the inductor becomes equal to its resistance, resulting in a purely resistive impedance.
2. Behavior of Capacitors:
- A capacitor is a device that stores energy in its electric field.
- At low frequencies, the reactance of a capacitor (Xc) is large, and its impedance (Z) is primarily determined by its capacitance (C).
- As the frequency increases, the reactance of the capacitor decreases. The reactance of a capacitor is given by the formula Xc = 1/(2πfC), where f is the frequency and C is the capacitance.
- When the frequency reaches the resonant frequency, the reactance of the capacitor becomes equal to its resistance, resulting in a purely resistive impedance.
3. Impedance of an AC Circuit:
- The impedance of an AC circuit is the total opposition to the flow of alternating current, taking into account both the resistance and reactance.
- The impedance is given by the formula Z = √(R^2 + (Xl - Xc)^2), where R is the resistance, Xl is the reactance of the inductor, and Xc is the reactance of the capacitor.
- When the frequency is at the resonant frequency, Xl = Xc, and the impedance is purely resistive.
- When the frequency is increased beyond the resonant frequency, Xl > Xc, resulting in an increase in the reactance term in the impedance formula. This leads to an increase in the overall impedance.
Based on the above explanations, we can conclude that when the frequency of an AC circuit resonating at 10 kHz is increased to 11 kHz:
- The reactance of the inductor will increase.
- The reactance of the capacitor will decrease.
- The reactance term in the impedance formula will increase, resulting in an overall increase in impedance.
- Since the reactance of the inductor is greater than the reactance of the capacitor, the impedance will become more inductive.
An ac circuit resonates at a frequency of 10 kHz. If its frequency is ...
Z(impedance)=√R2+(XL)2=√R2+(2πf)2
so, As frequency increases for inductive reactance , the impedance increases