NEET Alternating Currents — Set 1

Question 1

A transformer has $ N_p = 550 $, $ N_s = 1100 $. If $ V_p = 110 \, \text{V} $ (rms), what is the secondary voltage?

Accepted Answer

$ \frac{V_s}{V_p} = \frac{N_s}{N_p} $. $ V_s = V_p \times \frac{N_s}{N_p} = 110 \times \frac{1100}{550} = 220 \, \text{V} $.

Question 2

In a series LCR circuit at resonance, what is the relationship between the inductive and capacitive reactances?

Accepted Answer

At resonance in a series LCR circuit, the inductive reactance ($ X_L $) equals the capacitive reactance ($ X_C $). This balance cancels out the reactive components, making the impedance purely resistive and maximizing the current.

Question 3

A $ 254.6 \, \text{V} $ (peak) AC source is connected to a $ 90 \, \Omega $ resistor. What is the average power consumed?

Accepted Answer

RMS voltage: $ V = \frac{v_m}{\sqrt{2}} = \frac{254.6}{1.414} \approx 180 \, \text{V} $. RMS current: $ I = \frac{V}{R} = \frac{180}{90} = 2 \, \text{A} $. Average power: $ P = I^2 R = 2^2 \times 90 = 360 \, \text{W} $.

NEET Physics: Alternating Currents — Practice Set 1

Q1. A transformer has \( N_p = 550 \), \( N_s = 1100 \). If \( V_p = 110 \, \text{V} \) (rms), what is the secondary voltage?

Q2. In a series LCR circuit at resonance, what is the relationship between the inductive and capacitive reactances?

Q3. A \( 254.6 \, \text{V} \) (peak) AC source is connected to a \( 90 \, \Omega \) resistor. What is the average power consumed?

Q4. A series LCR circuit with \( R = 100 \, \Omega \), \( X_L = 130 \, \Omega \), \( X_C = 70 \, \Omega \) has a \( 300 \, \text{V} \) (rms) source. What is the power dissipated?

Q5. A transformer steps up \( 220 \, \text{V} \) to \( 440 \, \text{V} \). If the primary current is \( 10 \, \text{A} \), what is the secondary current?

Q6. A \( 60 \, \text{mH} \) inductor is connected to a \( 220 \, \text{V} \), \( 50 \, \text{Hz} \) AC source. What is the rms current?

Q7. A \( 85 \, \text{mH} \) inductor is connected to a \( 230 \, \text{V} \), \( 50 \, \text{Hz} \) source. What is the peak current?

Q8. In an AC circuit with only an inductor, what is the instantaneous power when the current is at its maximum?

Q9. In a series LCR circuit, under what condition does the circuit behave as if it has only resistance?

Q10. What is the behavior of the impedance in a series LCR circuit at very high frequencies?