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Question
A point positive charge is brought near an isolated conducting sphere (figure). The electric field is best given by ______.
Options
Solution
Explanation:
• Electric field lines come out of the positive charge and go into the negative charge.
• Tangent to the field line at any point gives the direction of the field at that point.
• Field lines are always normal to the conducting surface.
• Field lines do not exist inside a conductor.
The explanation to this problem can be done by keeping two things in mind.
- Concept of induction
- The electric field lines interact with a conducting body normally.
Let us discuss the phenomenon of induction involved in this case. When a positive point charge is brought near an isolated conducting sphere without touching the sphere, then the free electrons in the sphere are attracted toward the positive charge. Thus, the left surface of sphere has an excess of negative charge and the right surface of sphere has an excess of positive charge. It should be noted that both kinds of charges are bound in the metal sphere and cannot escape. They, therefore, reside on the surface of the sphere.
An electric field lines start from a positive point charge and ends at a negative charge induced on the left surface of sphere. Also, electric field line emerges from a positive charge, in case of a single charge and ends at infinity.
Here, all these conditions are fulfilled in Figure.
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