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NEET2010PhysicsDual Nature of MatterActual

A beam of cathode rays is subjected to crossed Electric ( E ) and Magnetic fields (B) . The fields are adjusted such that the beam is not deflected. The specific charge of the cathode rays is given by (where V is the potential difference between cathod and anode)

Options

  1. AB ^2 2 VE ^2
  2. B2 VB ^2 E ^2
  3. C2 VE ^2 ~B ^2
  4. DE ^2 2 VB ^2

Correct answer

D. E ^2 2 VB ^2

Step-by-step solution

As the electron beam is not deflected, then or aligned F _ m & = F _ e Bev & = Ee v & = E B aligned As the electron moves from cathode to anode, its potential energy at the cathode appears as its kinetic energy at the anode. If V is the potential difference between the anode and cathode, then potential energy of the electron at cathode = eV . Also, kinetic energy of the electron at anode = 1 2 mv ^2 . According to law of conservation of energy aligned 1 2 mv ^2 & = eV v & = 2 eV m aligned From Eqs. (i) and (ii), we

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