How does the Draconic Bloodline sorcerer's Elemental Affinity feature interact with the Scorching Ray spell?

Question

The Draconic Bloodline sorcerer's Elemental Affinity feature description (PHB, page 102) says:

...when you cast a spell that deals damage of the type associated with your draconic ancestry, you can add your Charisma modifier to one damage roll of that spell.

The Scorching Ray spell description (PHB, page 273) says:

You create three rays of fire and can hurl them at targets within range. You can hurl them at one target or several.

Make a ranged spell attack for each ray. On a hit, the target takes 2d6 fire damage.

Because I make an individual ranged spell attack for each ray of fire, and I have fire elemental affinity, can I add my Charisma modifier to each of the rays? Would it just impact one of the rays, because it's through one spell cast?

Answer 1

It would only apply to one ray

As you stated, the rules (post errata) state when and how you can use that feature (PHB, p. 102, bold added):

...when you cast a spell that deals damage of the type associated with your draconic ancestry, you can add you Charisma modifier to one damage roll of that spell.

The feature does not say that you can use this feature each time you make an attack, or each time you roll damage, but each time you cast a spell: and on one damage roll of that spell.

The spell Scorching Ray involves several attacks and (provided more than one hits) several damage rolls, but it's only one spell. You may use your elemental affinity feature on only one of those rolls.

Note that for a spell that has only one damage roll but affects multiple targets (like Fireball), the increase in damage from elemental affinity would apply to every target of the spell, because the spell has only one damage roll that applies to all the affected targets. But for a spell like Scorching Ray, you'll only be able to increase the damage once, because each ray has a separate damage roll.