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NCERT Class XII Chapter
Electric Charges and Fields
Questions With Solutions

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Question : 7
Total: 34
(a) An electrostatic field line is a continuous curve. That is, a field line cannot have sudden breaks. Why not?
(b) Explain why two field lines never cross each other at any point?
Solution:  

As,
→
FOA
 = -
→
FOC
 or
→
FOA
 +
→
FOC
 = 0 ... (i)
So, the net force on charge of + 1 μC at O is
→
F
 =
→
FOA
 +
→
FOB
 +
→
FOC
 +
→
FOD
 or
→
F
 = 0
A field line cannot have sudden breaks because the moving test charge never jumps from one position to the other.
(b) Two field lines never cross each other at any point, because if they do so, we will obtain two tangents pointing in two different directions of electric field at a point, which is not possible.
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