Verified Solution • 2025–26 Session moderate

QPages 121-124: Q12: HC Verma: Concepts of Physics - Volume 2 Electric Field Potential Pages 121-124: Q12 Solution: Two insulating small spheres are rubbed against each other and…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students frequently forget to take the square root of the charge squared ($q^2$) derived from Coulomb's law, leading to a massive error in the final electron count. Always isolate $q$ by taking the square root before dividing by the elementary charge $e$.

Two insulating small spheres are rubbed against each other and placed 1 cm apart. If they attract each other with a force of 0.1 N, how many electrons were transferred from one sphere to the other during rubbing?

Step-by-Step Verified Solution

**Answer:** Number of electrons transferred = 2.08 _ 10__. **Step-by-Step Explanation:** Given: F=0.1F = 0.1 N, r=10−2r = 10^{-2} m.
F=kq2r2⇒q2=Fr2k=0.1×10−49×109=1.11×10−15F = \frac{k q^2}{r^2} \Rightarrow q^2 = \frac{F r^2}{k} = \frac{0.1 \times 10^{-4}}{9 \times 10^9} = 1.11 \times 10^{-15}
q=3.33×10−8 Cq = 3.33 \times 10^{-8} \text{ C}
Number of electrons = q/e=3.33×10−8/1.6×10−19=2.08×1011q/e = 3.33 \times 10^{-8} / 1.6 \times 10^{-19} = 2.08 \times 10^{11} .

All Questions in this Chapter

QPage 119: Q1 QPage 119: Q2 QPage 119: Q3 QPage 119: Q4 QPage 119: Q5 QPage 119: Q6 QPage 119: Q7 QPage 119: Q8 QPage 119: Q9 QPage 119: Q10 QPage 119: Q11 QPage 119: Q12 QPage 119: Q13 QPage 119: Q14 QPage 120: Q1 QPage 120: Q2 QPage 120: Q3 QPage 120: Q4 QPage 120: Q5 QPage 120: Q6 QPage 120: Q7 QPage 120: Q8 QPages 119-120: Q1 QPages 119-120: Q2 QPages 119-120: Q3 QPages 119-120: Q4 QPages 119-120: Q5 QPages 119-120: Q6 QPages 119-120: Q7 QPages 119-120: Q8 QPages 119-120: Q9 QPages 121-124: Q1 QPages 121-124: Q2 QPages 121-124: Q3 QPages 121-124: Q4 QPages 121-124: Q5 QPages 121-124: Q6 QPages 121-124: Q7 QPages 121-124: Q8 QPages 121-124: Q9 QPages 121-124: Q10 QPages 121-124: Q11 QPages 121-124: Q12 QPages 121-124: Q13 QPages 121-124: Q14 QPages 121-124: Q15.1 QPages 121-124: Q15.2 QPages 121-124: Q16 QPages 121-124: Q17 QPages 121-124: Q18 QPages 121-124: Q19 QPages 121-124: Q20 QPages 121-124: Q21 QPages 121-124: Q22 QPages 121-124: Q23 QPages 121-124: Q24 QPages 121-124: Q25 QPages 121-124: Q26 QPages 121-124: Q27 QPages 121-124: Q28 QPages 121-124: Q29 QPages 121-124: Q30 QPages 121-124: Q31 QPages 121-124: Q32.1 QPages 121-124: Q32.2 QPages 121-124: Q32.3 QPages 121-124: Q33 QPages 121-124: Q34 QPages 121-124: Q35 QPages 121-124: Q36 QPages 121-124: Q37 QPages 121-124: Q38 QPages 121-124: Q39 QPages 121-124: Q40 QPages 121-124: Q41 QPages 121-124: Q42 QPages 121-124: Q43 QPages 121-124: Q44 QPages 121-124: Q45 QPages 121-124: Q46 QPages 121-124: Q47 QPages 121-124: Q48.1 QPages 121-124: Q48.2 QPages 121-124: Q48.3 QPages 121-124: Q48.4 QPages 121-124: Q49 QPages 121-124: Q50 QPages 121-124: Q51 QPages 121-124: Q52 QPages 121-124: Q53 QPages 121-124: Q54 QPages 121-124: Q55 QPages 121-124: Q56 QPages 121-124: Q57 QPages 121-124: Q58 QPages 121-124: Q59 QPages 121-124: Q60 QPages 121-124: Q61 QPages 121-124: Q62 QPages 121-124: Q63 QPages 121-124: Q64 QPages 121-124: Q65 QPages 121-124: Q66 QPages 121-124: Q67 QPages 121-124: Q68 QPages 121-124: Q69 QPages 121-124: Q70 QPages 121-124: Q71.1 QPages 121-124: Q71.2 QPages 121-124: Q71.3 QPages 121-124: Q72 QPages 121-124: Q73 QPages 121-124: Q74 QPages 121-124: Q75

Related Learning Resources & Exam Preparation

Chapter Practice Bank
Practice all topic-wise questions from Electric Field Potential
Reference Textbook Solutions
Explore complete chapter exercises for HC Verma: Concepts of Physics - Volume 2
Competitive PYQ Question Bank
Browse year-wise authentic previous years' questions with solutions
Authentic CBT Mock Tests
Simulate official exam environment with live timer and percentile scoring