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Dual Nature of Radiation and Matter question

2010 · Q153
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Dual Nature of Radiation and Matter question

2010 · Q153

NEETPhysicsDual Nature of Radiation and MatterMCQ+4 / −1
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 cathode and anode)
  1. A
    B22VE2{{{B^2}} \over {2V{E^2}}}2VE2B2​
  2. B
    2VB2E2{{2V{B^2}} \over {{E^2}}}E22VB2​
  3. C
    2VE2B2{{2V{E^2}} \over {{B^2}}}B22VE2​
  4. D
    E22VB2{{{E^2}} \over {2V{B^2}}}2VB2E2​
View written solutionFree

Correct answer: D

Force on electron due to = Force on electron due magnetic field to electric field

Bev = eE

⇒\Rightarrow⇒ v = EB{E \over B}BE​ .......(1)

If V is the potential difference between the anode and the cathode, then

12mv2{1 \over 2}m{v^2}21​mv2 = eV

⇒\Rightarrow⇒ em=v22V{e \over m} = {{{v^2}} \over {2V}}me​=2Vv2​ .....(2)

Substituting the value of v from equation (1) in equation (2), we get

em=E22VB2{e \over m} = {{{E^2}} \over {2V{B^2}}}me​=2VB2E2​

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