# Numerical Problems Based on Electric Potential Energy for Class 12 Physics

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## Numerical Problems Based on Electric Potential Energy for Class 12 Physics

Q.1. Find the amount of work done in arranging the three point charges, on the vertices of an equilateral triangle ABC, of side 10 cm, as shown in the adjacent figure.

(Ans. – 3.24 J)

Q.2. Two point charges +10μC and -lOμC are separated by a distance of 2.0 cm in air. (i) Calculate the potential energy of the system, assuming the zero of the potential energy to be at infinity. (ii) Draw an equipotential surface of the system.

(Ans. – 45 J)

Q.3. Three point charges + q, + 2q and Qare placed at the three vertices of an equilateral triangle. Find the value of charge Q (in terms of q), so that electric potential energy of the system is zero.

(Ans. Q = – 2q / 3)

Q.4. Two point charges A and B of values + 15 μC and + 9 μC are kept 18 cm apart in air. Calculate the work done when charge B is moved by 3 cm towards A.

(Ans. 1.35 J)

Q.5. Find the amount of work done in rotating an electric dipole, of dipole moment 3.2 × 10-8 Cm, from its position of stable equilibrium, to the position of unstable equilibrium, in a uniform electric field of intensity 104 N / C.

(Ans. 6.4 × 10-4J)

Q.6. Two point charges 20 × 10-6C and -4× 10-6C are separated by a distance of 50 cm in air. (i) Find the point on the line joining the charges, where the electric potential is zero, (ii) Also find the electrostatic potential energy of the system.

[Ans. (i) 41 cm from the charge of 20 × 10-6 C (ii) – 144 J]

## Why Students Fear Numerical Problems in Class 12 Physics?

The exam pattern for of previous exams generally consists of straightforward numerical problems that require students to apply basic mathematical concepts to solve problems. However, some common reasons for students’ fear of numerical problems in this class include:

1. Lack of practice: Students need to practice solving numerical problems regularly to build their confidence and understanding of the concepts. The exam pattern for Class 10 Science is relatively easy, but students need to ensure they are well-prepared for the exam by practicing regularly.
2. Fear of making mistakes: Since the exam pattern for Class 10 Science includes numerical problems, students may fear making mistakes while solving problems. Teachers should encourage students to understand the problem statement carefully and double-check their calculations to minimize errors.
3. Lack of conceptual clarity: Students may struggle with numerical problems if they do not have a clear understanding of the concepts involved. Teachers should ensure that students understand the fundamental concepts related to numerical problems to avoid confusion.
4. Difficulty in understanding the problem: Sometimes, students may struggle to understand the problem statement or may not know which formula to use. Teachers should guide students on how to identify the correct formula and approach to solve numerical problems.

## How to Prepare for Numerical Problems in Class 12 Physics?

Here are some tips for effective preparation:

1. Build a Strong Foundation: Students should ensure that they have a clear understanding of the underlying concepts involved in numerical problems. They should review their notes regularly and seek clarification from teachers if they have any doubts.
2. Practice Regularly: Solving numerical problems regularly is crucial to build confidence and improve problem-solving skills. Students should practice a variety of problems to develop their understanding of different concepts and formulas.
3. Focus on Understanding: Instead of rote memorization, students should focus on understanding the steps involved in solving numerical problems. This approach will help them tackle more complex problems.
4. Check for Mistakes: After solving numerical problems, students should double-check their calculations and identify any mistakes. This practice will help them avoid making careless errors and increase their accuracy.
5. Seek Help: If students are struggling with a particular concept or problem, they should seek help from teachers, tutors, or classmates. Clarifying doubts early on can prevent confusion and frustration later.
6. Mock Tests: Mock tests can help students assess their preparedness and identify areas for improvement. Students should take mock tests regularly and analyze their performance to identify weak areas.

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