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Concepts Of Physics MCQ Edition [Volume 2]
Exam
Concepts Of Physics MCQ Edition [Volume 2]
Subject
Physics
Chapter
Gauss's Law

Concepts Of Physics MCQ Edition [Volume 2] · Physics · Gauss's Law

A gold nucleus ( Z = 79 ) has a radius of approximately 7.0 × 10^...

A gold nucleus (Z=79Z = 79) has a radius of approximately 7.0×10−15 m7.0 \times 10^{-15} \text{ m}. Assuming its positive charge is uniformly distributed throughout the nuclear volume, determine the strength of the electric field at the surface of the nucleus.

Options

  1. A1.16×1021 N C−11.16 \times 10^{21} \text{ N C}^{-1}
  2. B2.32×1019 N C−12.32 \times 10^{19} \text{ N C}^{-1}
  3. C2.32×1021 N C−12.32 \times 10^{21} \text{ N C}^{-1}
  4. D9.28×1021 N C−19.28 \times 10^{21} \text{ N C}^{-1}

Correct answer

C. 2.32×1021 N C−12.32 \times 10^{21} \text{ N C}^{-1}

Step-by-step solution

The charge of the gold nucleus is given by q=Zeq = Ze, where Z=79Z = 79 and e=1.6×10−19 Ce = 1.6 \times 10^{-19} \text{ C}.

q=79×1.6×10−19 Cq = 79 \times 1.6 \times 10^{-19} \text{ C}

The electric field at the surface of a uniformly charged sphere of radius RR is given by:

E=14πϵ0qR2E = \dfrac{1}{4\pi\epsilon_0} \dfrac{q}{R^2}

Substituting the given values:

E=9×109×79×1.6×10−19(7.0×10−15)2E = \dfrac{9 \times 10^9 \times 79 \times 1.6 \times 10^{-19}}{(7.0 \times 10^{-15})^2}

E=1137.6×10−1049×10−30E = \dfrac{1137.6 \times 10^{-10}}{49 \times 10^{-30}}

E=23.216×1020 N C−1E = 23.216 \times 10^{20} \text{ N C}^{-1}

E≈2.32×1021 N C−1E \approx 2.32 \times 10^{21} \text{ N C}^{-1}
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