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Moving Charges And Magnetism

Question
CBSEENPH12037669

A charge particle with charge q enters a region of constant E and B with velocity V perpendicular to both E and B, and comes out without any charge in magnitude or direction of V, then establish a relation between V, E and B.

Solution

A charged particle goes undeflected when, 
                     qE = qvB 

                  v = E/B 

The force due to electric field and magnetic field are acting on the charged particle and will oppose each other if v is along E × B 
Now, v = E BB2 =EB sin 90oB2 = E × BB2  
Therefore, 

              v = E × BB2 
which is the required relation . Error: timeout waiting for response.