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QPages 121-124: Q5: HC Verma: Concepts of Physics - Volume 2 Electric Field Potential Pages 121-124: Q5 Solution: Find the electric force between two protons separated by a…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often plug $r=1$ directly into Coulomb's law, forgetting that 1 fermi = $10^{-15}\,$m; this misses a $10^{30}$ factor and yields an absurd force. Always convert distances to SI units before squaring them.

Find the electric force between two protons separated by a distance of 1 fermi 1 fermi=10−15 m1 \text{ fermi} = 10^{-15} \text{ m}). The protons in a nucleus remain at a separation of this order.

Step-by-Step Verified Solution

**Answer:** Force = 230.4 N. **Step-BY-Step Explanation:** Given: q=1.6×10−19q = 1.6 \times 10^{-19} C, r=1r = 1 fermi =10−15= 10^{-15} m.
F=kq2r2=9×109×(1.6×10−19)2(10−15)2=9×109×2.56×10−3810−30=230.4 NF = \frac{k q^2}{r^2} = \frac{9 \times 10^9 \times (1.6 \times 10^{-19})^2}{(10^{-15})^2} = \frac{9 \times 10^9 \times 2.56 \times 10^{-38}}{10^{-30}} = 230.4 \text{ N}

All Questions in this Chapter

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