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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

Separated by a distance of 2.00 cm , two large conducting plates...

Separated by a distance of 2.00 cm2.00 \text{ cm}, two large conducting plates are positioned parallel to one another. An electron released from rest near one plate travels to the opposite plate in 2.002.00 microseconds. Determine the surface charge density on the inner surfaces.

Options

  1. A2.53×10−13 C/m22.53 \times 10^{-13} \text{ C/m}^2
  2. B5.05×10−13 C/m25.05 \times 10^{-13} \text{ C/m}^2
  3. C5.05×10−11 C/m25.05 \times 10^{-11} \text{ C/m}^2
  4. D1.01×10−12 C/m21.01 \times 10^{-12} \text{ C/m}^2

Correct answer

B. 5.05×10−13 C/m25.05 \times 10^{-13} \text{ C/m}^2

Step-by-step solution

Given the distance between the plates, d=2.00 cm=0.02 md = 2.00 \text{ cm} = 0.02 \text{ m}, and the time taken by the electron, t=2.00 \mus=2.00×10−6 st = 2.00 \text{ \mu s} = 2.00 \times 10^{-6} \text{ s}.

Using the kinematic equation for a particle starting from rest:
d=12at2d = \dfrac{1}{2} a t^2

Solving for acceleration aa:
a=2dt2=2×0.02(2.00×10−6)2=0.044.00×10−12=1010 m/s2a = \dfrac{2d}{t^2} = \dfrac{2 \times 0.02}{(2.00 \times 10^{-6})^2} = \dfrac{0.04}{4.00 \times 10^{-12}} = 10^{10} \text{ m/s}^2

The force experienced by the electron in the uniform electric field EE is F=eE=meaF = eE = m_e a.
Thus, the electric field between the plates is:
E=meae=9.11×10−31×10101.60×10−19=5.69×10−2 V/mE = \dfrac{m_e a}{e} = \dfrac{9.11 \times 10^{-31} \times 10^{10}}{1.60 \times 10^{-19}} = 5.69 \times 10^{-2} \text{ V/m}

For two large parallel conducting plates with opposite charges, the electric field in the region between them is given by:
E=σϵ0E = \dfrac{\sigma}{\epsilon_0}
where σ\sigma is the surface charge density on the inner surfaces.

Solving for σ\sigma:
σ=ϵ0E=(8.85×10−12 C2/N⋅m2)×(5.69×10−2 V/m)\sigma = \epsilon_0 E = (8.85 \times 10^{-12} \text{ C}^2/\text{N}\cdot\text{m}^2) \times (5.69 \times 10^{-2} \text{ V/m})
σ≈5.04×10−13 C/m2\sigma \approx 5.04 \times 10^{-13} \text{ C/m}^2

The closest matching option is 5.05×10−13 C/m25.05 \times 10^{-13} \text{ C/m}^2.

Answer: 5.05×10−13 C/m25.05 \times 10^{-13} \text{ C/m}^2
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