The Basic Performance Index is satisfied by launching the projectile any distance. The Extra Performance Index involves launching the projectile several feet. Calculate the EPI with the following formula. Magnetic field around conducting wire. Field is strongest very close to the wire.
Electromagnetic things operate by making magnetic fields with wire that is conducting electricity.
Magnetic fields are invisible, but can be felt if two solid magnets are held close together but not allowed to touch. You will feel either attraction or repulsion. This works well in a demonstration. The magnetic field that is induced around a single, current carrying wire is shown in Figure 1. When a single strand of wire is connected to a battery, a current flows through the wire, and at the same time a magnetic field is produced right around it.