Q144 / 160 · TS EAMCET 2022 (18 Jul Shift 2) · Physics

A large metal plate has a surface charge density of 8.85×10-6 C m-2. An electron having initial kinetic energy of 8×10-17 J is moving towards the center of the plate. If the electron stops just before reaching the plate then the initial distance between the electron and the plate is [Take ε0=8.85×10-12 C2 N m-2]

  • Correct answer
    A
    0.5 mm
  • B
    0.1 mm
  • C
    0.2 cm
  • D
    0.02 cm

Solution

Electric field due to an infinite sheet of charge having surface density σ is E=σε0.

Now using energy conservation we can write,

gain in potential energy = loss in kinetic energy

⇒qEd=12mv2⇒1.6×10-19σε0d=8×10-17⇒d=8×10-178.85×10-121.6×10-198.85×10-6=0.5 mm

Hence, the correct answer is option: 'A'.

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