Question 25
The diagram shows a non-uniform electric field near a positively
charged and a negatively charged sphere.
Four electrons, A, B, C and D, are shown at
different positions in the field.
On which electron is
the direction of the force on the electron shown correctly?
Reference: Past Exam Paper – November 2011 Paper 12 Q31
Solution:
Answer:
A.
The direction of electric
field lines is the direction of the force on a positive charge. That is,
the direction is from (away) a positive charge towards a negative charge. It
represents the force acting on a positive charge (a positive charge would be
attracted towards a negative charge).
An electron, which has a
negative charge, will be attracted towards the positive sphere [B incorrect], NOT towards the negative charge [D incorrect] since like
charges repel and unlike charges attract.
The resultant field
between the two charges is non-uniform.
In a non-uniform
electric field, the direction of the electric field on a charge at any
specific point is given by tangent to the electric field line at that point in
the electric field. [C incorrect since it is not a tangent]
Choice C represents the
direction of the force on the charge if only the positive charge was present.
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