SATHEE: alternating-currents Question 20

alternating-currents Question 20

Question: Q. 5. (i) When an $a c$ source is connected to an ideal inductor shows that the average power supplied by the source over a complete cycle is zero.

(ii) A lamp is connected in series with an inductor and an $a c$ source. What happens to the brightness of the lamp when the key is plugged in and an iron rod is inserted inside the inductor? Explain.

U] [O.D. I, II, III 2016]

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Solution:

Ans. (i)

$P_{a v} = I_{a v} \times V_{a v} \cos ϕ$

For an ideal inductor, $ϕ = \frac{π}{2}$

$\begin{aligned} ∴ & P_{a v} = I_{a v} \times V_{a v} \cos \frac{π}{2} & P_{a v} = 0 \end{aligned}$

$1 / 2$

(ii) Brightness decreases. Because as iron rod is inserted, inductance increases, hence the current will decrease with decrease in brightness.

Detailed Answer :

(i) The average power supplied by the source over a complete cycle is

$P_{a v} = E_{r m s} \times I_{r m s} \times \cos ϕ$

When the circuit carries an ideal inductor, then the phase difference between the current and voltage is $π$ $\overset{―}{2}$

In case of pure inductive circuit, $ϕ = \frac{π}{2} \Rightarrow \cos \frac{π}{2} = 0$ So power dissipated $= 0$

Hence, when an ac source is connected to an ideal inductor, the average power supplied by the source over a complete cycleis zero.

[CBSE Marking Scheme 2016]

AI Q. 6. An inductor $L$ of inductance $X_{L}$ is connected in series with a bulb $B$ and an $a c$ source. How would brightness of the bulb change when (i) number of turns in the inductor is reduced, (ii) an iron rod is inserted in the inductor and (iii) a capacitor of reactance $X_{C} = X_{L}$ is inserted in series in the circuit. Justify your answer in each case.

U] [Delhi I, II, III 2015]

Alternating Currents

alternating-currents Question 20

Detailed Answer :

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Alternating Currents

alternating-currents Question 20

Detailed Answer :

Table of Contents

Engineering Preparation

Medical Preparation

NCERT Books & Solutions

Important Resources

Other Resources

Syllabus

Test Platform

Sample Mock Test

Mentorship

NCERT Exercise Video Solution

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