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KVPY2012PhysicsAtomic Physics

A stream of photons having energy 3 eV each impinges on a potassium surface. The work function of potassium is 2.3 eV . The emerging photo-electrons are slowed down by a copper plate placed 5 ~mm away. If the potential difference between the two metal plates is 1 ~V , the maximum distance the electrons can move away from the potassium surface before being turned back is-

Options

  1. A3.5 ~mm
  2. B1.5 ~mm
  3. C2.5 ~mm
  4. D5.0 ~mm

Correct answer

A. 3.5 ~mm

Step-by-step solution

K =3-2.3=0.7 eV , S = K eE and E = V / d

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