When you imbue your weapon with arcane energy, you can expend evocation power to deal energy damage instead of normal damage.

Prerequisite(s): Arcane Strike, Spell Focus (evocation), 1st-level eldritch knight

Benefit: When you activate your Arcane Strike feat, you can expend an unused evocation spell that you have prepared or a spell slot of a level in which you know at least one evocation spell (for spontaneous casters). If you do, choose an energy type. All of the normal damage dealt by your attack becomes damage of that energy type. In addition, your attack deals 1 additional damage of that type per level of the spell expended. These effects last until your arcane strike ability ends on your next turn.