There is only one case where the electric field force does not do work, that is, the charge moves in the direction perpendicular to the electric field line (on the equipotential surface), otherwise it will do work. When moving along the electric field line (pay attention to whether it moves along a straight line), the electric field force does positive work, while when moving against the electric field line, the electric field force does negative work. The work done by electric field force can be calculated in the following two ways:

1, calculated according to the definition of work W=Fscosθ.

In middle school, limited to the mathematical foundation, F is required to be a constant force in the formula, so this method is only suitable for calculating the work done by electric field force in a uniform electric field. θ is the included angle between the direction of charge movement and the direction of electric field force, and θ is less than 90 degrees when moving along the direction of electric field line; When moving against the electric field line, θ > 90 degrees; When perpendicular to the electric field line, θ = 90 degrees.

2. calculate with WAB=qUAB.

This method has two processing methods:

First, strict symbolic operation, both Q and UAB consider positive and negative, and the positive and negative of W directly indicates the positive and negative of electric field force.

Second, only the absolute value is taken for calculation, so W is only the value of work, and the positive or negative work can be judged by mechanical knowledge.