Questions for Electric Field (JC) Set 1

In discussing electric fields, the terms ‘electric field strength’, ‘electric potential’ and ‘potential gradient’ are used.

Which statement about these terms is correct?

  1. Electric potential and potential gradient are both scalar quantities.
  2. Electric field strength at a point is the work done in bringing unit positive charge from infinity to the point.
  3. The potential gradient at a point is numerically equal to the electric field strenght at that point.
  4. Unit potential gradient exists between any two points, if one joule of work is done in transporting one coulomb of charge between the points.

$$E =-\frac{dV}{dr}$$

Answer: 3

A +3.0 C point charge is initially stationary at a point X in a uniform electric field of strength 5.0 V m-1. It is then moved within the field 3.0 m parallel to the field and then 4.0 m perpendicular to the field lines to point Y as shown in the diagram below.

electric field qn 2

  1. 5.0 J
  2. 45.0 J
  3. 75.0 J
  4. 105.0 J

There is no work done by the field when the charge moves perpendicularly to the field lines. (No change in potential when moving perpendicularly to field lines)
Hence, work done by the field = Fd = qEd = (3.0)(5.0)(3.0) = 45J

Answer: 2

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