 # NCERT Exemplar Solutions for Class 12 Physics - Chapter 7: Alternating Current (LA)

Physics NCERT Exemplar Solutions are available in this article. Here you will get solutions of Chapter 7 Alternating Current (Long Answer Type Question i.e., question number 7.27 to 7.31). These questions are important for CBSE board exam and other competitive exams. NCERT Exemplar Solutions for Class 12 Physics - Chapter 7: Alternating Current (LA)

NCERT Exemplar Solutions for Class 12 Physics Chapter 7 Alternating Current are available here. In this article, you will get solutions of long answer type questions (i.e. question number 7.21 to 7.26).

We have already provided solutions of multiple choice questions with single correct answer (MCQ I), multiple choice questions with multiple correct answers (MCQ II), very short answer type questions (VSA) and short answer type question (SA). You can access them from links given below

NCERT Exemplar Solutions for Class 12 Physics - Chapter 7: Alternating Current (MCQ I)

NCERT Exemplar Solutions for Class 12 Physics - Chapter 7: Alternating Current (MCQ II)

NCERT Exemplar Solutions for Class 12 Physics - Chapter 7: Alternating Current (VSA)

NCERT Exemplar Solutions for Class 12 Physics - Chapter 7: Alternating Current (SA)

NCERT Exemplar Solutions for CBSE Class 12 Physics, Chapter 7 (from question number 7.27 to 7.31) are given below:

Question 7.27: Solution 7.27: Question 7.28:

1MW power is to be delivered from a power station to a town 10 km away. One uses a pair of Cu wires of radius 0.5 cm for this purpose. Calculate the fraction of ohmic losses to power transmitted if

(i) power is transmitted at 220V. Comment on the feasibility of doing this.

(ii) a step-up transformer is used to boost the voltage to 11000 V, power transmitted, then a step-down transformer is used to bring voltage to 220 V.

Cu = 1.7 × 10–8 SI unit)

Solution 7.28: Question 7.29:

Consider the LCR circuit shown in Fig 7.6. Find the net current i and the phase of i. Show that i = v/Z. Find the impedance Z for this circuit. Solution 7.29: Question 7.30:

For an LCR circuit driven at frequency ω, the equation reads

L (di/dt) + Ri + q/C = vi = vm sin ωt

(i) Multiply the equation by i and simplify where possible.

(ii) Interpret each term physically.

(iii) Cast the equation in the form of a conservation of energy statement.

(iv) Intergrate the equation over one cycle to find that the phase difference between v and i must be acute.

Solution 7.30: Question 7.31:

In the LCR circuit shown in Fig 7.7, the ac driving voltage is v = vm sin ωt.

(i) Write down the equation of motion for q (t).

(ii) At t = t0, the voltage source stops and R is short circuited. Now write down how much energy is stored in each of L and C.

(iii) Describe subsequent motion of charges. Solution 7.31 NCERT Solutions for CBSE Class 12 Physics: All Chapters