An electric field acts into the plane of the paper - AQA - A-Level Physics - Question 16 - 2019 - Paper 2

When an electron enters an electric field at 90° to the field lines, the force it experiences is defined by the equation:

$F = qE$

where $F$ is the force, $q$ is the charge of the electron (which is negative), and $E$ is the electric field strength. The force is directed opposite to the direction of the electric field due to the negative charge of the electron. Therefore, the correct answer is:

D. opposite to the direction of the field.