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Electric Charges And Fields

Question
CBSEENPH12039225
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An electric dipole is held in a uniform electric field.

(i) Show that the net force acting on it is zero.

(ii) The dipole is aligned parallel to the field. Find the work done in rotating it through the angle of 180°.

Solution

i)  Dipole moment of dipole is given by,  
i) 
open vertical bar straight p with rightwards harpoon with barb upwards on top close vertical bar space equals space q space x space left parenthesis 2 a right parenthesis

Force on –q at A = -qE

Force on +q at B = + qE

So,

Net force = qE – qE = 0
 

ii)
Work done on dipole is given by, 
straight W space equals space increment straight U space equals space PE space left parenthesis cos space straight theta subscript 1 space minus cos space straight theta subscript 2 right parenthesis space space space equals space PE space left parenthesis cos space 0 to the power of straight o space minus space cos space 180 to the power of straight o right parenthesis straight W space equals space 2 space PE

Some More Questions From Electric Charges and Fields Chapter

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? 

Figure shows tracks of three charged particles in a uniform electrostatic field. Give the signs of the three charges. Which particle has the highest charge to mass ratio?

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