Question

The diagram shows a positive charge moving in a magnetic field.

A field of circles labeled B. There is a positively charged particle with a velocity vector pointing left labeled v.
In which direction is the magnetic force acting on the charge?

into the screen
out of the screen
up
down

Answer 1

You need the dot/cross on the circles to know B’s sense. Use F = q v × B (right‑hand rule) for a positive charge:

- If the circles have a dot (B out of the page) → v (left) × B (out) gives force upward.
- If the circles have a cross (B into the page) → v (left) × B (in) gives force downward.

Tell me whether the circles show a dot or cross and I’ll pick the single answer.