# Minqi 19 May 2016 - 2

## Question

The figure shows a full scale diagram of equipotential lines of an electric field, with potential difference of 3.0 V between adjacent lines.

What is the closest estimate of the magnitude and direction of the field strength at P along the dotted line?

The electric field lines are from the positive charge to the negative charge, hence, the direction of the electric field strength is towards the left.

To calculate the electric field strength, we use the following relationship:

Since the diagram is drawn full-scale, we need to measure the distance d as shown in the diagram below using a ruler.

The potential difference between the 2 lines are 6.0 V.

Hence the electric field strength is $$\left | E \right | = \left | 6.0 \over d \right |$$ towards the left.