NEET Alternating Currents — Set 9

Question 1

In an LCR series circuit, what happens to the circuit’s behavior when the frequency is significantly above the resonant frequency?

Accepted Answer

Above resonance, $ X_L = \omega L $ becomes much larger than $ X_C = \frac{1}{\omega C} $, making the net reactance positive. The circuit behaves as predominantly inductive, with the current lagging the voltage.

Question 2

A transformer has $ N_p = 500 $, $ N_s = 250 $. If $ V_s = 120 \, \text{V} $ (rms), what is the primary voltage?

Accepted Answer

$ \frac{V_s}{V_p} = \frac{N_s}{N_p} $. $ V_p = V_s \times \frac{N_p}{N_s} = 120 \times \frac{500}{250} = 240 \, \text{V} $.

Question 3

In an AC circuit with only an inductor, what is the phase relationship between the current and the voltage?

Accepted Answer

In a purely inductive AC circuit, the current lags the voltage by 90°. This is because the inductor opposes changes in current, causing the current to reach its peak after the voltage.

NEET Physics: Alternating Currents — Practice Set 9

Q1. In an LCR series circuit, what happens to the circuit’s behavior when the frequency is significantly above the resonant frequency?

Q2. A transformer has \( N_p = 500 \), \( N_s = 250 \). If \( V_s = 120 \, \text{V} \) (rms), what is the primary voltage?

Q3. In an AC circuit with only an inductor, what is the phase relationship between the current and the voltage?

Q4. A transformer has \( N_p = 800 \), \( N_s = 400 \). If \( V_s = 110 \, \text{V} \) (rms), what is the primary voltage?

Q5. A \( 70 \, \Omega \) resistor and \( 30 \, \mu\text{F} \) capacitor are in series with a \( 220 \, \text{V} \), \( 50 \, \text{Hz} \) source. What is the impedance?

Q6. A series LCR circuit with \( R = 60 \, \Omega \) is at resonance with a \( 240 \, \text{V} \) (rms) source. What is the rms current?

Q7. A series LCR circuit has \( R = 35 \, \Omega \), \( X_L = 60 \, \Omega \), \( X_C = 25 \, \Omega \). What is the power factor?

Q8. In an AC circuit with only a capacitor, what happens to the impedance if the capacitance is decreased?

Q9. A \( 230 \, \text{V} \) (rms) source supplies a \( 115 \, \Omega \) resistor. What is the peak current?

Q10. A \( 22 \, \mu\text{F} \) capacitor is connected to a \( 220 \, \text{V} \), \( 50 \, \text{Hz} \) AC source. What is the rms current?