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BITSAT 2023Paper 1
Exam
BITSAT
Year
2023
Paper
Paper 1
Subject
Physics
Chapter
Electrostatics

BITSAT 2023 · Paper 1 · Physics · Electrostatics

The force between two small charged spheres having charges of 1 ×...

The force between two small charged spheres having charges of 1×10−7C1 \times 10^{-7} \mathrm{C} and 2×10−7C2 \times 10^{-7} \mathrm{C} placed 20cm20 \mathrm{ cm} apart in air is

Options

  1. A4.5×10−2N4.5 \times 10^{-2} \mathrm{ N}
  2. B5.4×10−2N5.4 \times 10^{-2} \mathrm{ N}
  3. C4.5×10−3N4.5 \times 10^{-3} \mathrm{ N}
  4. D5.4×10−3N5.4 \times 10^{-3} \mathrm{ N}

Correct answer

C. 4.5×10−3N4.5 \times 10^{-3} \mathrm{ N}

Step-by-step solution

Here, q1=1×10−7C,q2q_1=1 \times 10^{-7} \mathrm{C}, q_2 and 2×10−7C2 \times 10^{-7} \mathrm{C}, r=20cm=20×10−2mr=20 \mathrm{ cm}=20 \times 10^{-2} \mathrm{ m}
F=q1q24πε0r2=9×109×1×10−7×2×10−7(20×10−2)2F=\frac{q_1 q_2}{4 \pi \varepsilon_0 r^2}=\frac{9 \times 10^9 \times 1 \times 10^{-7} \times 2 \times 10^{-7}}{\left(20 \times 10^{-2}\right)^2}
=4.5×10−3N=4.5 \times 10^{-3} N
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