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Electric Fields

Q1. The diagram shows lines of force for the electric field surrounding two charged objects L and M.

(a) Explain why the lines of force shown in in the diagram above cannot represent a gravitational field.

The gravitational force is only an attractive force - never repulsive. Therefore a gravitational field should only indicate attraction to a body, and the lines of force should only be going towards an object. The lines of force going away from L therefore show it cannot be a gravitational field.

[1 mark]

(b)

(i) Deduce which object L or M has a charge with the greater magnitude.

L has the greatest density of field lines, it therefore has the greater charge magnitude.

(ii) Deduce which object L or M has a positive charge.

L has field lines emanating from it. The field line shows the direction unit positive charge would move and that would be away from a positive charge.

[2 marks]

(c) Draw, on the diagram above, an equipotential line that passes through point N.

Do not extend your line beyond the given field lines.

The drawn line should cross the field lines at right angles.

To award the first mark the marker was told to only look at the 4 lines of force close to N.

Essentially the range is from a vertical line to one that curves only slightly in order to cross the 4 field lines close to N at right angles.

This mark can also be given if a right angle symbol appears on the diagram at any field crossing of the drawn line.

A mark was given if the line is symmetrical top to bottom and it bends to the left.

[2 marks]

(5 marks)