Numerical Problems Based on Capacitance of Capacitors for Class 12 Physics
Q.1. Two metallic conductors have net charges of + 70 pC and – 70 pC, which result in a potential difference of 20 V between them. What is the capacitance of the system?  Â
(Ans. 3.5 pF)
Q.2. A spherical capacitor has an inner sphere of radius 9 cm and an outer sphere of radius 10 cm. The outer sphere is earthed and the inner sphere is charged. What is the capacitance of the capacitor?
(Ans. 0.1 nF)
Q.3. A parallel plate air capacitor consists of two circular plates of diameter 8 cm. At what distance should the plates be held so as to have the same capacitance as that of a sphere of diameter 20 cm?
(Ans. 4 mm)
Q.4.  The stratosphere acts as a conducting layer for the earth. If the stratosphere extends beyond 50 km from the surface of the earth, then calculate the capacitance of the spherical capacitor formed between stratosphere and earth’s surface. Take radius of the earth as 6400 km.  Â
(Ans. 0.092 F)
Q.5. A capacitor of 20 μF is charged to a potential of 10 kV. Find the charge accumulated on each plate of the capacitor.   Â
(Ans. 0.2 C)
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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:
- 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.
- 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.
- 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.
- 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:
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
