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## Homework Statement

beam of protons moving in +x direction at speed v

electric field is perpendicular to magnetic field

magnetic field in +y direction

no deflection

What direction/sign has the electric field?

## Homework Equations

not looking for numerical solutions

## The Attempt at a Solution

There's no deflection, the magnetic and electric force have same magnitude, but opposing directions, correct?

The magnetic force is perpendicular to the magnetic field, while the electric force is in the direction of the electric field.

How do I then find the direction of the electric field?

+x and -x are perpendicular to +y. Let's say the magnetic force has a magnitude of 5, the electric force would be -5. Is the direction of the magnetic force -x, i.e. magnitude of -5 and thus the electric force a direction of +x, i.e. magnitude of 5?