Charged particles experience a force in an electric field.

Electric fields exist around charged particles and between charged parallel plates.

Field lines always point in the direction a positive charge would move if placed there.

The closer the field lines the stronger the electric field.

These field lines can be used to determine the path that a charged particle will take when placed in any of these systems.

Voltage (potential difference) is the work done per unit charge.

1 $V$ means 1 $J$ of work done per 1 $C$ of charge. This is shown in the equation below which relates charge, voltage, and energy.

The relationships below can be used to solve problems involving the charge, mass, speed, and energy of a charged particle in an electric field and the potential difference through which it moves.

$$ W=QV $$

$$ E_k=\dfrac{1}{2}mv^2 $$

A moving charge produces a magnetic field.

Particle accelerators are designed to accelerate particles to very high speeds for us in experiments.

Electric fields can be used to accelerate charged particles.

Magnetic fields can be used to deflect charged particles — steer and focus them into position.

Particle accelerators also involve high-energy collisions of charged particles to produce other particles.

For example, in a cyclotron an alternating voltage is used to ensure the electrical field acting on the proton as it crosses the gap is always acting in the correct direction so that the proton accelerates in the correct direction.

Or in a linear accelerator, where an alternating source is used to ensure the direction of the electric field is always constant — in the correct forward direction — when the electron passes between alternate gaps.

In a linear accelerator, the length of the tubes increases as you go along because as the particle speeds up it travels a farther distance in the same time.