Shown is an apparatus for studying the properties of electrons. Electrons from an emitter F pass through a hole in G and then move into a region where crossed electric (L) and magnetic (M) fields are applied. The spacing between the electric field plates at L is 1 mm. Various target materials can be placed at W. The electrons are detected at a phosphor coated screen labeled x-y. One scale unit on the screen equals 1 cm.
For the permanent magnet B = 0.1 T. What is the potential across L?